u/DecentYeti

I live in a quiet residential neighborhood and there is a gym near my house. At 7AM local time I walked over and took the gym from yellow to blue. As I was walking home less than 5 mins later the gym was taken and an entire squad of yellows were back in the gym with the same Pokemon I just defeated. How is this possible? There were more trainers at the gym than there are houses in the vicinity, and I had a view of the gym my whole walk, no one was there. I just started playing last week so I am new and maybe this is something very normal, but it seemed suspicious to me. I have also held this gym for 3 days straight until last night when it was taken around 3-4AM.