It's not. "Generalising" means taking an individual observation, and drawing conclusions about all cases (or a large class of cases). I think you're saying that "I'm not unusual" is a canonical example of generalization, i.e. claiming that my case applies to a large class. But I didn't make that claim.
It's possible that my observation was wrong - that I am unusual. But that would mean that the majority of my recent colleagues were also unusual, because I don't think more than a tiny fraction of them had Github accounts.
Given a specimen case, and absent evidence to the contrary, it's a mistake to suppose that specimen case is unique or unusual. It's much more likely to be common. And if you discover similar cases, then it's definitely not unique, and unlikely to be unusual.
But I think this is litigious point-scoring; I say that having a Github account is not a good discriminator for "software developer". If you disagree, please explain why, instead of claiming that I contradicted myself by saying I wasn't generalising in a post that contained a "blatant generalisation".
[Note: I'm a brit, trying to transition gracefully from "-ise" to "-ize"; I'm having trouble internali[zs]ing the rules.]