From the launch commentary, the rocket is designed to do a 180 at that altitude for the separation event. So a couple extra rotations isn’t going to hurt anything. Additionally, air density at 100k ft is ~1/80th of sea level, which helps.
You mean it should have separated on a 180-flip? Boosting rocket all the way there to break and start orbiting in opposite direction? No way. F9 doesn't do that. The booster should have flipped without starship. That was mistake on commentator side - they were talking all the time like everything is normal. Even when we all saw it started to twist, commentator sayd something like: waiting on separation.
Anyways, the stress rocket experiences in a position like that is such that they break up, because its not designed for positions like that - we have seen that on failing rockets videos. This one did multiple flips with upper stage attached that shouldn't be there on rotation. And thats great :)
