Isn't Flame Body Heatran illegal?

Question

Ok so in White 2 I just found a Heatran with Flame Body.
How did this happen?
This is not a ROM and it is a legal game that was purchased at a store. It is not a Heatran from the DW. I ran into it at Reversal mountain and did not receive it from a trade and this also happened a few times before. I do not hack and do not own a working Action Replay.

Comments

Is it a ROM?

Answer 1

Yes it's illegal.

Reason why?

Heatran hasn't even been released with it's Hidden Ability Flame Body.

So I can only assume that the reason you encountered Heatran with Flame Body is because your game has been hacked some time in the past with some type of modifier code.

Source: Bulbapedia and Showdown.