Exactly that.

I wasn't reachable by phone for company related stuff outside my regular working hours unless I had on-call-duty, which means it was working hours.

I don't get why people would be proud about not setting boundaries.

It really depends on where you want to steer your career. There's some roles, especially in management, where "working hours only" isn't really an option; if you aspire to one of those you've gotta convince people you'll do what's necessary.