I've seen incorrect information on Serebii before. For example, in USUM, they mentioned a Pokémon that appeared in the Photo Finder but didn't. I think the error is still there today, and it's known that the Pokémon mentioned doesn't exist, but rather a pre-evolution of it.
If I'm not mistaken, it's Bewear that they say can be photographed on Route 8, but it isn't.
https://www.serebii.net/ultrasunultramoon/pokefinder.shtml
This is just one example, but I've seen other errors like this there and wouldn't be surprised if this one was another, since nowhere else I looked did this trainer appear in Infinite Z-A Royale.