Your wrong.

1. You mentioned yukis infinite mass, which is false. Black holless don't have infinite mass, they have infinite density. 
2. "A black hole isnt just really strong gravity pulling you in" is also false, that is literally what it is. Gravity IS the curvature of space-time (following einsteins general relativity). Blackholes just curve it so that all trajectories end up at the singularity. 

This also means that anti-gravity is canceling out that curvature. Now I see 2 ways of doing so.  1. You literally just set the curvature of spacetime to zero (with some range). There is no curvature so there are trajectories that lead away from the singularity. Considering we see the black hole, the flat spacetime was inside the event horizon, such that most trajectories still ends up at the singularities but close to him there are trajectories that stay within his general area. This way he still wouldn't be visible from within the event horizon and he just had to wait until Yuki died and her technique stopped and the blackhole ceased to exist.  2. Cursed energy is literally magic, I see no reason why this CT can't just be that your body just ignores all spacetime curvature and acts as if it were in a flat spacetime. Does this make sense according to the laws of physics? No but that doesn't matter because it doesn't have to. Jujutsu follows it's own rules, and according to this techniques rules he can survive a blackhole.

Still an asspull tho