300m off the end of a 2700m runway realistically means either a) retardation devices (brakes, spoilers, reverse) failed or not deployed or b) very deep and/or fast touchdown.
From passenger reports, it seems the brakes and reversers were in use, so that leaves b). To get 300m on grass/mud, you're looking at leaving the tarmac at 80kts+ groundspeed.
Reminds me a bit of
AA331 or even
Air India Express 812. Results would have been similar if the overrun at LYS wasn't so benign.