I checked the story, it seems that it was an human mistake that they settled it incorrect.
Your bet was lost, as the match result was including overtime.
cashout option is a nice option, but you cant blame bookmakers if this option is not available.
I dont see any problem here in this case.
Its a big problem. If he knew the game was still running he could easy bet the other side to have a profit (in case cashout was unavailable) .
They made him think he won so he didnt take these possible actions. Its super misleading in my eyes.