If the "mites" you saw are snake mites, one quick treatment with reptile relief probably didn't do the job. You'll want to watch very closely for recurrence. Provent-A-Mite (PAM) is the best way to handle mites. Do a search on this site on its use.

They generally don't come in bedding, although it is possible if the bedding came from a store that is infested. There are a lot of other bugs that can occasionally come with the bedding. Keep an eye in the water bowl for little black specks. If you find any, look at them under magnification, a microscope if one is available, or strong magnifying glass otherwise. You may want to google snake mite images so you know what to look for.

Steve