Well, strictly speaking it's true. Same reason why Manaphy makes Phione. Whether or not something breeds and what it does or doesn't produce is entirely on what's coded, and has nothing to do with egg groups. Egg groups just determine what pokemon are able to be stuck together to make the children they're programmed to.
Elsewise we'd have, what, some kind of horrifying eldritch-location for a daycare while we mercilessly pump a ditto and magneton to produce hordes of random genderless pokemon, possibly up to and including the controllers of time, space, life, death, and even creation.
If you put a wad of bubblegum on a horseshoe magnet, you *probably* shouldn't start spontaneously birthing gods. One would hope, at least.
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