Being vulnerable can be great and helpful when forming personal relationships. A manager asking their direct reports to be (personally) vulnerable in a professional setting, in front of a group, is inappropriate.

While I agree that it wasn't forced (and I know that I would personally have no problem sticking to whatever level of sharing I was comfortable with), I bet you that at least one person on that team felt uncomfortable with it, but also felt like they could be penalized in some way (even just socially) if they didn't share. That's not ok.

If you can't forge bonds with your teammates without your boss asking people to share vulnerable moments during a team meeting, there are deeper problems that this sort of exercise is not going to address.

From my most recent job, I have quite a few strong friendships that we've maintained over the years, even though we've all left that company years ago. But most (if not all) of my so-called friendships with coworkers at other jobs faded quickly after one of us left the company. That's pretty normal, and there's nothing wrong with that. There's also nothing wrong with having a vibrant social life outside of your colleagues, and not really being interested in those colleagues beyond acquaintance level.