A "co-pilot" on a 152? Sounds more like a pilot who lost his/her medical, went up with an instructor and decided to end it all. Very sad.
I`ve flown the 152s quite a bit, and you don`t just fall out of them. They`re hard to get into and even harder to get out of. Of course accidents can happen, and yes, those doors can sometimes pop open during any phase of flight.