As a middle aged dude who's been in tech for 25 years, I can say that literally all of my close friends at this point in life were previous coworkers.

Especially if you relocate away from your hometown for a job, I'm not sure why that would be surprising to anyone. You spend at least 8 hours a day with these people, it only makes sense you'd eventually build some connections with them. And as the parent post points out, it certainly makes the days more enjoyable when you've built healthy relationships with your peers.

And come to think of it, most people 30+ I know seem to have friend groups of almost exclusively current or former coworkers. I don't think I'm by any means unique.