Deoxys in Pokemon Colosseum's Tower Colosseum?

[SwagKey]

I may need a bit of insight into this.

A while back I was using a GBA registered team to go through Tower Colosseum's Level 100 Doubles in Battle Mode, and the final trainer had a Deoxys-Defense that I didn't think too much of at the time. It wasn't until recently when I randomly decided to look up the rosters of each individual trainer where I discovered nobody had it listed as available in the trainer's party. Can someone look into this? Everywhere I looked came up empty and I'm confused out of my mind about it.