Probably every trainer in the Pkmn world has a Ditto, no one who knows that Pokémon would remain a virgin. Just show him a picture and he transforms, some can even do it without weird eyes.

But seriously I think it's a flaw GF overlooked, they should have said he only turns into other Pokémon.
They literally created the Sex Pokémon without realizing it, not to mention its potential uses in crime.