Wow I wish someone would go out of their way for me like that when I've felt that way! (and I mean actually felt that way, not throwing a party and going on self help forums threatening to top myself). I had a break down for 8 months last year where I never talked to anyone or answered my phone, nobody really came running to my aid. What I wouldn't give for someone to do what you did.
What this person did was idiotic and cruel, and takes the help away from people genuinely need it. When one person who tries to help gets tricked, there are a number of people who genuinely needed that help who will now not get it.
Please don't beat yourself up over it, it's okay to be mad at this person and feel fooled, but that doesn't mean you didn't do the right thing that someone who needed it would have been forever thankful for.

As for suicidal posts, I do think it should be allowed. But there should be restrictions with the 'I'm going to kill myself right now' posts. Being someone who has been suicidal, I know full well how a person like that thinks. Support is very lacking these days. You look up suicide on the net and it will usually come up with posts on being punished by God if you do it, or posts from people calling someone and idiot who's looking for attention and telling them to just do it and stop complaining.
If you are in that frame of mind it's very hard to stay focused enough to look for proper help. You want help, then when you get it you don't want it, but you still kind of do, and you want to ask for help but you can't ask for help and you want to die but you don't want to die and every negative thing that has occurred in your life runs through your mind at once and you don't know what you want to do and you wish someone would just appear and make it all better but even if they came you would barely be able to share how you feel so that they can help you because you can't make up your mind and...... You just go nuts with confusion.

Someone who is in a suicidal frame of mind is NOT someone who can think logically. Every living thing has the instinct of survival, our mission as a living thing is to stay alive. It is an instinct programmed into the minds of every living thing from day dot. When someone is in such a mental state that they are literally going against their own instincts of survival, that person is NOT thinking logically or rationally. That person has a different thought process to someone who is not suicidal. They have a completely different thought process to THEMSELVES if they were thinking logically.
And it can be very hard to ask for help. How do you call a friend or relative and say 'I want to die'?
When I get down, and I have been a few times lately, I find it impossible to do anything more than go on Facebook and say 'I need a hug'. I cannot for the life of me ask for help, other than online. And part of that reason is because not many people are willing to go out of their way to help. I know WHY that is, because I've been on that end of the stick too, and it's frustrating as hell to deal with someone who is in that state. But better to go to someone who knows than someone who doesn't because all you ever hear about suicidal people from those who aren't is that they are being selfish. That infuriates me immensely. It is NOT selfish to be suicidal. 99.9% of people who are suicidal do NOT want to die, they are just emotionally exhausted and need things to end- death sometimes seems the only solution to a never ending torture. A lot of people who are suicidal think they deserve it, or they think people are better off without them, or they just want someone to notice them. We all need human interaction and understanding, so sometimes being attention seeking isn't about wanting to be centre of attention, it's about wanting someone to just see you.
But even as someone who has been suicidal and has a family filled with people who are the same, if someone comes to me wanting to die, I wouldn't know the first thing to say to them. There isn't really any right thing to say in that situation. It's scary, exhausting and frustrating to look after someone who's like that.
Don't try to help someone if you genuinely can't, as sad as it is nobody is obliged to look after someone like that. If you can’t, then don’t. But if you can, then do, because for some people this is the only place anybody has to go to. Some people don’t have phones to call a helpline. Some people don’t have friends or family who will rush to them. Some people find it easier to express how they feel impersonally rather than by speaking it directly. Some people have shut everyone out of their lives and can’t exactly call someone for help. Some people are just looking for others who relate. Some people just don’t know. Of course there is then the suicidal curse of nobody answering their phones and suddenly having a life when you so desperately need it.
This is the only place some people have.