I could believe that hot staging might've affected the booster, since it seemed to blow up right as it tried to light the engines again for boostback. But I don't think the ship would've made it so long if it were seriously damaged by the hotstaging.
Damage to the grid fins mechanism is a potential failure mode here. Even a small amount of damage to the flight control systems could make the procedure uncontrollable and eventually trigger the FTS.
At this altitude, the vehicle is pretty much in the vacuum and grid fins have absolutely no control authority. It could have resulted in failure later on but not at that point where the booster blew up.
Saw that Scott Manley video that came out right after that and it looks like fuel issues to engines probably caused it. All but one engine started up, but they started failing after that.
Then it's not hot staging but maybe sloshing of fuel in the tank just simply.
How could hot staging affect the engines of the booster? If it affected the tanks then the three engines still running through separation would also fail so no flip-around could be possible with no thrust to go with.
The booster experienced a rapid unscheduled disassembly after boostback burn following the successful stage separation