Emerald Ore generated in Plains biome

So, there's this world I've been playing for quite a while (so this may be hard/impossible to reproduce if the seed isn't broken already). I'm not sure what caused that, but yesterday while I was mining I found a emerald ore out of Mountains biome. There's a Mountains biome (kinda far away from there) that could have caused it do happen, but still, it was predominantly Plains and not a Montains biome either way. Not sure if it's an addition from the newer snapshots (couldn't play/read about 19w35a and 19w36a), but well, if it is please correct me. The world was initially created at 1.14.