I can tell you why you feel put off by that behavior: it's because they're being fake. As you said yourself, they definitely don't know you after that little bit of time so to say something like that is clearly just them lying to try to seem nice or into you or whatever. I had one lately that told me he was "spellbound" after just a couple days messaging back and forth where we have little in common. I stopped messaging after that. It makes me feel sick that someone could say that when they don't know me and what little they do know is entirely opposite of them in almost every way. I do most of my looking for guys online (too terrified to do it IRL, plus I hate my area) and 90% of the ones that contact me through these sites have either very little written on their profile or have literally nothing in common with me, if not both. Why bother? Don't be so damn desperate fellas. As badly as I want to be with someone, I want a good relationship, not something fleeting that will never become anything.

tl;dr? You're not alone in those feels. Trust the feels. Being fake isn't cool.