Weed won’t make your stomach larger, so no, it would certainly not be a performance enhancing drug.
If anything, weed would make the person have a snack beforehand, or not care about their strategy, or dry out their mouth.
I cannot see how weed would ever be an enhancing drug in this sport, let alone in any sport (I’m looking at you, Ross Rebagliati). Eating contests aren’t about eating, they’re about putting food inside of you at an extremely fast rate.