Low volume garbage set. Seen this a few times. They can get in easy, but there is not enough garbage/debris to climb out. They have probably been in this dumpster before and had no problems getting out because there was enough trash to climb on to exit.
I got called out to my local Hilton hotel for this once. I arrived to find 8 raccoons in the dumpster with a low volume of trash , unable to get out. I jumped right in the dumpster to the shock of the employees there who gathered to watch. Made short work out of it with my Ketch-all pole as I stuffed them into 4 large Wickencamp box traps. I had to jump inside the dumpster as my Ketch-all pole didn't have enough reach as it was a taller dumpster and I couldn't reach the back. Easy work , quick (20mins on site) and profitable.
I've talked to several garbage truck drivers who tell me the regularly have raccoons bail real fast as soon they hear the forks going into the pockets as they get ready to lift the dumpster.