The headline is misleading.

He's being charged with violating the Lacey Act which prohibits owning/hunting/trading certain plants or wildlife. Today it's mainly used to punish people for importing non-native species of animals.

I can't know exactly what parts of the Lacey Act he was accused of violating (it's extremely broad), but it would make sense to me that he's being charged because of the unlicensed import of the argali sheep. It's not the cross-breeding that's illegal, it's what he's cross-breeding and how he got it that's illegal.