So this AI called Miley just popped up out of nowhere on Route 118 (next to the Berry Fields).
Now I'm not complaining about extra training for my Gyarados but she wasn't there before. Is this the case or did I just not see her?
No it's not a glitch. Delinquent Miley is an actual trainer on that Route, with a Cacnea and a Mightyena. You most probably just didn't see her.
Hope I helped!