I tried looking for a site that has "psychic fangs" and "kommo-o" within the same breath, and I think only theirs showed up. (the rest seemed to be "how to counter kommo-o" sets etc)
In any case, they're wrong :3
yeah, in most scenarios, a mon cannot have a TR move, without the corresponding TR flag (that shows it was taught the move). Thus why it wasn't legal without the flag.
(Cause the move have no reason to be learned without the flag)
Anyway, happy playing :3