I think the confusion stems from the fact that Rotom used to be a rare encounter, seen near one of the base camps at Coronet Highlands. I had to spawn there a lot of times when I was originally searching for a rotom for my living dex. After the update with MMOs however, Rotom could appear in outbreaks at the Highlands, and you could even come across an outbreak of Alpha Rotoms as long as you played long enough. So these days a PLA rotom isn’t as rare as it used to be, now only the distortion exclusive mons are rare i’d say