Sometimes users like that pop up. It's unexplained, but I'm guessing it's a glitch in GTS. I've seen it before. Sorry for the wishy-washy answer, but I don't really think there is much of an explanation.
Edit: since I wasn't clear enough I guess and I took a little time to think back into retrospect:
I meant encountering them like that on the PSS. I'm guessing hacking or cartridge reading failure like smiley said in comments. Another guess is PSS server internally glitched because of the load.
(Edit2: Edited out ORAS trainer idea, didn't see was Kalos)