Then, yes, it's legit. Fact that it made the poketransfer already meant so. Since it is an event Pokemon, it shoul have a cherish ball, the OT you mentioned, the level 5 and of course, its event location. Since it has perfect Ivs, however, it is undeniably a hack. Since pokebank did not detect the Jirachi as a hack... It all means you're good. It's a legal hack. In a way, it's completely legit.