I haven't yet met any adults with Autism, other than online. I have no idea what it would be like to meet a bunch all at once in real life, so I can't really identify until such a time comes. I have though, seen quite a lot of posts similar to yours, so I know the way you feel is not uncommon at all. We are all so very different from each other that I think it's not beyond comprehension that a lot of us are probably like mismatched puzzle pieces that simply don't fit together.
I came here just about two years ago expecting everyone here to understand me. Boy was I ever wrong. But it's not a problem for me. Yeah, a ton of users here didn't understand my way of thinking, but a lot of that came from my own crappy communication skills, probably added to their own communication styles that just plain didn't match my own. Over time here, I've come to learn that it's okay to not be understood sometimes, that it's okay not to understand others at times. It's all fine. I don't have to impress anybody, and nobody has to impress me. The one thing almost all of us have in common is that we are all different, unique, and there is nothing wrong with that.
I almost left this forum within the first few weeks of being here. I don't even remember exactly why. I do remember that I was feeling here just as you are describing in your post. But I didn't leave, and that feeling eventually passed. I would imagine the same is probably true meeting other Autistics in real life. I bet a lot of the people you saw at those meet ups felt just as out of place as you did. If it were me, I'd give it more time. I would go anyway. Don't forget that we've probably ALL felt weird, outcast, sidelined, and generally shunned at one time or another. That is the one thing about yourself they probably do understand.
I bet if you give it more of a chance, you'll find that it's worth the effort, even if you spend long time not talking to anyone. Yeah, the people there may SEEM more social than you are, but I bet once you get to know them you're going to start learning you aren't as different from them as you think you are. Not that you are the same, but I bet you think you are more different than you really are. The only way to know is go and spend some time listening for a while. After a while, I wouldn't be surprised if you hear something that makes you want to speak up.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...