Maybe I could jump in and answer?

Just your post here has a really big clue. I will misspeak. Please bear with me. But you come off as really aggressive. ("How do you know?" - why have a go at someone when you're the one asking the questions? if you're not going to trust that you'll get informed answers, here, why post here at all?) Avoidant people are pretty shy. Now, you poke us with a stick, we will defend ourselves. But - and, yes, this is stereotypical, but you're asking for impressions - generally BPD has a reputation for being aggressive, bold, in your face, and AvPD has a reputation of being meek, quiet, reserved.

When I say aggressive, I mean, you posted that and directed it to someone else, but you were so confrontational that I wanted to go hide in my cave and it wasn't even aimed at me. Yes, I understand I'm sticking my nose in where it doesn't belong maybe. But if I saw a post directed to me like that, it would take me days to respond, so here I am butting in, and maybe getting you a response much more quickly. Who knows. And I'm not saying I'm speaking for the other person, just giving my impression.

Also, AvPD is very commonly self-diagnosed incorrectly. It's almost impossible to have the distance to really see what's going on. People tend to attribute qualities that happen every once in a while, or there is an urge to stay away from confrontations or something like that. They confuse the term "avoidant" for "avoids something." Totally different things.

It can be very damaging to self-diagnose as avoidant, because there is no treatment or cure. Borderline - that's great! Seems maybe on the surface like you don't want that, but I've known Borderlines who have been treated and they're just about normal. Yes, it's a lot of work doing the therapy. But you'll be normal! Don't limit yourself before you even get started.

Maybe you're just an introverted Borderline. Sounds like an oxymoron, but they actually do exist.