I just found exactly the same thing on my drivers side quarter panel, same type of crack in the paint and the filler lifting as the metal was not sanded correctly.
LOL, that is so typical of your average auto body shop. They do not want to spend time straightening the sheet metal, just put a ton of mud on it and get it out fast...
Same place but less deep dent with ancient tin repair on my 71 hood. That and a few rust fixes in the latch and twist locks hole kept me busy a few weekends.
It's gonna be fun!
Good luck!