or, as simpler explanation: the footage was captured from a device which was running the modded game.

edit: or, from the stream of the person using modded game.

Since you've already been corrected on the assumption that players used/saw the nude mod, I'll just point out: Fighting game tournaments almost never use "lan". Two players sit in front of one console and one monitor, and plug in their own controllers. Super high budget tournaments like EVO might use dual-console setups for finals day, but when you're chewing through an open bracket it's just silly to double the required amount of hardware per station.