can someone explain to me how this happened cuz I got this two times in one run, looks p neat actually :D

and here is the video FailFish

Well, I know of 2 ways to softlock the game.

1: The game softlocks, if baron misses himself with a projectile shot. (which happened in your case)

I believe, this happens,. because the game waits until the projectile reaches either the left or the right end of the screen. But as baron attacks himself there is no horizontal distance to be covered and thus the projectile doesn't move (actually it moves slowly up for some reason). As a result, the projectile will never reach the right/left end of the screen and thus softlocks the game.

2: if you hold space during a cutscene-only-stage, before the cutscene starts.

Apparently, this can skip the cutscene without ending the stage thus softlocking the game. On combat stages the doesn't happen, I guess, this is, because the "end combat" trigger is not related to the cutscene that is skipped. To avoid this, don't hold spacebar on cutscene-only stages until the text actually appears. Once the cutscene startet, it is safe to skip it.

Yeah, I also had that 2nd one once, and I sort of figured out why it caused the animation but not why it would softlock, now I understand though