This seems completely unrelated to actually catching pets, as it has nothing to do with catching pets; you can have 30 pets just by buying them off of vendors, the blizzard store, etc.
As someone who is addicted to catching 'em all, it makes no sense to me that this achievement isn't linked to the number of pets one captures, instead being linked to leveling pets.
So... I would like the achievement to be changed. It should be: Capturing 400 unique pets awards you the Pristine Trap.
As I said, leveling pets and catching pets are two completely different aspects of Pet Battles, and are mostly unrelated. You can level 30 pets to 25 without having caught a single one in the wild.
Please make the achievement to increase the accuracy of pet traps linked to how many pets we've caught, and not how many we've leveled.