I also read those BUK systems pick up the identifier pings all passenger planes have so they don’t shoot them by accident. So I don’t know what to guess on that, they fired anyways “cause it had spies on it” as the rebels claimed or it was planned shoot down to blame on Ukrainians and it backfired on the Ruskies. ??
Or maybe Putin wants the area cleared of all aircraft for an soon to be mounted larger invasion with complete air control. Doubtful the Ukraine Air Force would last long in such an invasion. Evil times.