Most likely. You can see where the mistake could occur. Wrong liquid put in to some vials, or installed wrong color cap onto finished vials.
Lyophilization process is:
-Vial filled with peptide liquid
-Rubber lyophilization stopper put in
-Freeze dryer "sucks" moisture out through stopper, leaving dry puck in vacuum sealed vial
-Metal collar with cap is crimped onto vial
I've seen this happen a couple of times before, and it happens more often than we realize because you can only be certain of what's in the vial thats actually been tested. There's no guarantee of what's in the rest of the kit. This isn't Pfizer. It's more like having a McDonalds worker make your drugs.
Luckily Reta mixed into a Tirz kit isn't a catastrophe. I doubt most people would notice. Most "wrong" peptides wouldn't be a major threat to health.
But if it had been 30mg Semaglutide, or 10mg MT-2, someone who thought they were injecting 15mg Tirz would've ended up in the hospital.