Good idea, especially when it's just only Garchomp. And of course, Professor Sycamore IS very protective of his Mach Pokemon. Heck, he might ignore the fact he is defenseless without his Pokemon.

Also, there is another possibility. Maybe he got knocked out alone and he became a sleeper agent with his Garchomp not knowing what happened.

Of course, that's my imagination gone wild on that possibility, but you get the point.