Theres actually another topic i found on this topic:
https://community.ld4all.com/t/why-do-we-enter-rem-during-naps/35454
It basically says that out of the 3 stages of Rem sleep that you go through at night, during a nap you only go through the first as rather than deep sleeping, your body is simple trying to have a small break. The other post is in a bit more detail.