Shiranui had sent Saisei out while the poacher was gloating and the Mewtwo got a lock on her mind before she made her escape.  Both the trainer and Mewtwo came down from their treetop cover and along with Zoro and Bakeru got the cages together.

"She can't have gone far with a Mega Garchomp unless she had a Pokémon who knows Teleport handy," Shiranui stated.
"[i]I locked onto her mind while she was gloating and got the info from her partner while Mike was punching him,[/i]" Saisei added.  The Mewtwo warned Mike, "[i]The path of a berserker is not a path for you.[/i]"