Rarity of Wild Pokémon with Pre-learned TM Moves?

[Alzandre]

I caught a Nidoran Male with Iron Tail in Shade Forest yesterday. Just wondering what the rarity is of something like that happening?

[A_Wild_Noob_Appeared]

When you search for a Pokemon using the DexNav, they will have at least one Egg Move (Iron Tail is an Egg Move for Nidoran).

[Alzandre]

Ah! That makes sense. Thanks