If you were the casino manager would you fire the casino worker for interfering with your business or would you ban the gambler from visiting the casino?
If I was the manager of the casino, I will not fire my worker but I'll tell him privately not to yell gambler like that. It can be done politely and privately so it will have a better situation for the whole casino. About the gambler, it depends on the policy of the casino. As I have no idea about the policy of the casino for such case, I cant say anything how to deal with the gambler but I think banning the gambler from visiting the casino wont help him as he can move to other casino. We do not even know about the actual financial status of the gambler. Even if he keeps losing everyday but it does not mean that it is a problem for the gambler.
Without a doubt he did not managed the situation with the necessary tact that the situation required, however we do not know the whole circumstances behind it, it seems they were relatives and he was worried about the behavior of this gambler in particular and he could not contain himself anymore, however as you said I think it would be a mistake to fire him and at most I think he should be taught how to deal with difficult customers so something like this does not happen again.