ok what just happened

Sorry, I can't see the video, can you tell me what exactly happened?

I long jumped into a goomba at the bit after the three coins just before the wallkicks at the start and clipped into the bit with the question mark block and died somehow.

Oh, that. You probably hit a corner and the game tried to clip you out of it by going up. Assuming you were using the autosplitter, the crash check activated and killed you so the game wouldn't crash.

that's exactly what happened. thx for the insight

It's just the "softlock bug"

it happens when you enter a platform without an end