Regular blastoisenite not in purity mode

[Former user]

I've made it to the perfection base, defeated Taen (1 pokemon left XD), and gotten the mega ring and when it went to the place where I was suppsoed to get the delta blastoisenite, it was a regular blastoisenite. I checked on videos, wikis, and forum and reddit posts to see where all the megastones where, and they all said it was inside the perfection base. I'm not sure if this is a bug or not (please forgive me if it isn't). Thanks!