Both to blame but more the driver of the moving vehicle. You are only supposed to open your door once you've checked it's clear (as a general rule) - stops you dooring people on bikes for one, although that's not an issue here. I'm hazarding even if the parked car's driver did check if it was clear the moving car's driver was going too fast for the conditions and wouldn't have been seen?
I have impression the door was open before the nose of the car entered the parking spot... but I couldn't see that for sure from my angle.
They were both harping at each other when I left. I kind of lean towards equally to blame, but not sure. I have a teen about to get his license, must remember to tell him this story. Nobody wants so much hassle.