It seems like Rebble (the board) really overplayed their hand.
From what they posted, it seems like they wanted more control over what Core was doing, deciding that the best way to do that was to try and hold the app store data hostage.
Now, with the Core app open sourced and multiple app store repos supported, Rebble's position will likely be greatly diminished from what it could have been if they had been satisfied with what they had. I guess in the end though, the outcome was a net win for everyone (fully open source apps), so it works out.
I spent some time on their Discord chatting and trying to nudge them towards a healthier approach.
Many of them seem to think that PebbleOS was released just for them (they quote the Google press release), and so reading between the lines I really do think they feel at some level that code has been "stolen" from them. Which is ridiculous (and I said so) but if they think it's true then it explains their actions much more clearly than any other explanation I've found (or they've elucidated).
My best understanding (which I've extrapolated from what I've learned) is that they had all these plans of being a scrappy team who worked together on PebbleOS in their spare time, as friends, and Eric capitalising a company of paid developers has made all those plans redundant - so they've been powering through the five stages of grief in coming to terms with that while everyone else has been celebrating the return of Pebble.
From what they posted, it seems like they wanted more control over what Core was doing, deciding that the best way to do that was to try and hold the app store data hostage.
Now, with the Core app open sourced and multiple app store repos supported, Rebble's position will likely be greatly diminished from what it could have been if they had been satisfied with what they had. I guess in the end though, the outcome was a net win for everyone (fully open source apps), so it works out.