"Completely successful" would've been reaching orbit. They didn't expect to get that far, but this was still a far cry from a complete success. Only milestones cleared are countdown, launch, and stable flight in fixed attitude - which still leaves a lot of big ones on the way to orbit (controlled pitchover, max-Q, stage sep, second stage ignition and operation, payload fairing separation, orbital insertion, payload separation at the very least).
The rocket started oscillating before. I believe it was pure coincidence that the launch termination system kicked in when they started the pitchover manoeuvre.