I agree with this. If a casino wishes to prevent certain bets from being made, they should simply disable the option. By accepting a bet, they are expressing their readiness to take on the risk involved in the outcome of the event being bet on. If the bookie subsequently voids a winning bet, they are retroactively avoiding the very risk they had agreed to take on. This is fundamentally unfair and goes against the principles of a fair and honest betting system.

I can't say who is right and who is wrong in your case, but if a casino lacks transparency and provides a inadequate explanation, they should be deemed untrustworthy and avoided completely.