Sounds a lot like my ex, always putting me in a 'damsel in distress' role and trying to fix thing for me or make them better. We were both software developers and he too tried to make my career better, except he played a role in making it worse. He did it with the best of intentions but it is neither useful nor respectful towards the independence of a partner, a good relationship is a bond between equals.

I ended up ignoring my gut feeling, making mistake I'd otherwise not have made, and while I might still have made mistakes regardless, it is better for someone to make them on their own. It also saves some future resentment towards that person, and all the bad stuff for both parties that follows from it.

Simply said, if what he says is right about your career, you should be able to find evidence elsewhere. Even if it is a terrible field, there's still the fact of what feels right to you. A good career is about more than pay or prestige or other superficial measurements for success. If you are happy with what you are doing, stick with it. And if you have doubts, seek out professional career advice. Not from random Joe in the bar who seemed to be coming on rather strong. I mean it is possible he just felt like playing the mentor, but it would have been a whole lot different had you just been casually chatting about careers at a networking event, right? Also people who are genuinely interested in helping tend to be constructive, not destructive. I'd hazard a small hunch he might be projecting too, seeing his own problems in you. But how do you know it wasn't him that was being a shitty employee in a good field?

I'd not accept the Facebook request. Suggest he adds you on LinkedIn instead, keep it professional. If he is legit about professional interest, he should be ok with that. Considering he already snooped on you, look him up on there, see what professional circle within your city he is in. I'd certainly not go work for his company, stick with where you are. Keep the conversation to work and career and see how long he holds up. If he's just trying to get in your pants, it probably will not last long, or he will keep trying at which point you can simply state you are no longer feeling comfortable with being in contact. Yeah, he can react very malicious if you do that, but if you do it politely you have your own written evidence should he decide to go after you. Most likely though, he'll get bored or take the hint and just flake.

As for being normal in the industry, I mostly find myself treated as "one of the boys". Other men are interested in talking about mutual interests. There's always a few that will either look down on you, or objectify you, or a combination of both. But women can be equally ugly to each other and use sexism in that too. Don't let one bad apple worry you. Do what you like and what feels right, and trust in your gut. It might not always be right, but it often has a reason, which in this case is that this guy comes across as having an agenda. It's up to the critical mind after to gather the evidence and figure it out.