It's typical outsider gossip tier bullshit.
I've worked in the industry for over 15 years (it'd be 17, but I took a year off from burnout back in 2008), and, like, people leave companies, change positions, or leave the industry completely for so many different reasons. Most of us don't plan on being in our current positions in the industry indefinitely. I know it's hard to fathom for some, but, surprise, a lot of us have dreams/ambitions beyond our current role. I don't plan on being a game designer forever. I have other career goals that I'm working towards, and when I'm at a place where I can achieve those goals (whether with my current studio, or if, for some reason, another studio), then I'll pursue those goals. It's not always some juicy tidbit that causes industry folk to move around. It literally happens all of the time, and most of it is never really remarked upon, because, honestly, it's just not worth remarking on. It's generally fairly rare that it's "bad blood" as the reason why people leave. One of the things about this industry is that, especially in the US, and especially here in LA, is that it's very small.
A lot of us have worked with each other across a variety of different studios and publishers over the years. Burning bridges isn't something most of us try to do, because, honestly, you never know who you're going to be working with in the future. Most departures are very amicable and friendly, with the door being open for a return in the future if the stars align again. I know I can't think of any times where someone was, say, a complete and utter asshole, so we were happy to see the back end of them when they left. Besides, word gets around when it comes to those types of personalities in the industry, and they often have a hard time finding work at other studios if they're legitimately "problematic" employees.
Drew left Insomniac for reasons that are his own. He then left the Initiative to return to Insomniac for reasons that are his own. Like, why does it really matter? He's doing what he loves, and is happy to be back at a home he had for, what, a decade or so?
Hell, even at our studio, we've had people leave and come back, and it's always a celebratory time when former employees come back, because we hated to see them go in the first place, but we were also happy that they were pursuing other opportunities in their careers, even though it meant they had to leave us.