It is NOT okay for a parent to ask their teenage child to "strip down" for a spanking, no matter what is being used belt/or brush. This parent obviously reacted emotionally to an upsetting situation, and should have taken a longer break to calm down before carrying out a punishment. I think the length of time involved in the actual "punishment" here is a bit much as well, although the OP doesn't go into detail about the amount of force used, or whether welts or bruising were results of this action.
There is a fine line between punishment and abuse, and the only person that can define whether the line was crossed based on the information given, is the person involved. If the OP feels as if they've been abused, they need to talk to someone objective about it. School counselor, pastor, someone with the capacity to provide help and not make the situation worse by taking one side or the other automatically.