Looks alot more like Cloud was trying to go for a grab once mario lands, but Mario was able to get up from Landing Lag and jab, since Cloud extended his hurtbox into Mario (in which he had his jab out by then) Cloud got hit by the back part of the jab....since that happens in this game alot.
Though why Cloud was tripped to the floor. It's hard to tell. My thoughts are that is has alot to do with the ledge.
but Maybe there was some sort of momentum carried from the Perfect Sheilded Mario Bair, that affects affects cloud in such a way that triggers a ceiling glitch similar to this?
It can easily be something else, like since it seems like a cluster of cross ups and character hurtbox shifting going on in that split second, where Cloud is the one that ends up closest to the ledge, so when Mario's jab hits him trying to grab (which Cloud crosses into mario) makes some weird effect where cloud is hit, and tripped off the ledge from Jab's Hitstun, but also hit ON the stage so it immediately interrupts the falling animation, resulting in the immediate 'slam' > jab lock to happen.
Just my opinion from looking at it. Can't test anything atm unfortunately....
