Un-Training Puppy Pads?

i have a problem that i can’t find advice for anywhere else. i adopted my dog 3 months ago now, he just turned a year old. the shelter said he was housebroken (we had what i would assume was a regression in the beginning..new environment, routine, and all, ya know?) but it didn’t take him long to get the hang of it and he hasn’t had many problems since. i take him to my moms a few days a week to watch him while i’m at work, the days i don’t he is crated. he has been having “accidents” in the house, and by “accidents” i mean he will go to the bathroom in the house 5 minutes after having him outside for quite a bit of time. she has dogs as well and i recently learned he has been using the puppy pads she puts out for her dogs. they take their dogs outside regularly so i’m not sure why they have puppy pads? but i’m thinking this may be the problem. do i have to completely stop taking him to her house and restart on potty training? i’m asking in here because all of the things i can find are advice on how to un-train them from using puppy pads by moving them closer and closer to the door but i don’t have them in my house and refuse to use them unless medically necessary. any and all advice would be greatly appreciated 🙂