so I cut out on treats yesterday and he still didn't want his food. I put hot water on it and it just didn't make a difference

do they stop getting excited at their food at a certain age?
he's been on this natural food for about 4 months now, and only thing that I can think of was last week he went for a sleepover at my boyfriends house. He has an old english sheepdog who eats the food that Riley used to eat (tasty food but only because its filled with junk) and apparently he kept stealing the big dogs food...could that be it?