If you value the cooperation and goodwill of your lab partner in any matter that does not touch directly upon his grade, stop it. Stop everything you're doing to try to pry the introvert out of his shell. Stop trying to analyze his handwriting without also matching that to his actual actions. Stop analyzing his handwriting when he's trying to communicate with you, and start reading the words he's writing. Stop assuming that 90% accuracy means that he's among that 90%.
Even though he doesn't follow the things that you've got right about him (he doesn't think you're right at all on some topics, but from what he says I think you're about 90% right but the 10% you have wrong is crucial to the whole picture) he's still the world's foremost existing expert on what goes inside that head of his.
He doesn't want to socialize with you. If he wanted to socialize, he'd do it with one of his friends, or at the very least someone who respects him and his autonomy. He doesn't want to socialize with anyone who will use cheap psychological tricks to get reactions from him without a real understanding of him or a real willingness to listen and learn rather than dismiss him quickly into a predetermined category.
I don't have your psychology degrees. I don't have any experience in practice. I do know this man, and I know how to get him to open up to me, and in doing so I've managed to avoid pissing him off the way you're doing. So stop it.
So, yeah, Darkside's lab partner is old enough to be his mother and is an expert on everything, and is trying to become an expert on him, and failing quite completely. In the commiseration, I did explain the two psychological tricks that I use on him with relative frequency, because it's only fair that he knows that I know this about him.
When he reads my mood wrong, and tries to cheer me up when I'm just feeling quiet but not sad, I will sometimes make him work for that smile. And I told him that he smiles like a fool when he gets it. I conceded that perhaps it might not look like smiling like a fool to a stranger, but if you know him, you know his expressions. No, it's not a smirk with one corner of the mouth. It's both corners. (He was a little dubious on that one, but I assured him, it does happen.)
Also, I declared, I know how to make him open up. He was very dubious on this front, so I explained. He'll be talking, and I'll be silent, and then he'll go silent, and I'll stay silent, and then when he starts talking again he'll have opened up. Ah. "Listening" was what he called that one, and it's a bit of a lost art in many bits of the US.
I don't think he'd known, quite, that I knew these things about him. I'm not entirely sure that he'd known them about himself, especially that smile. He is deep, and we shall never come to the end of each other.