There are many religions out there which are small and shady as anything. One of them is well known from its "elders" indulgence in certain dehumanizing things. Hence a religious person may not always be a good person. Gambling though is known to bring bad outcomes to those who get addicted to it and thus religions abhor it. But there are many religious people who regularly gamble and lose money in it, without any remorse.

Hence we should not see the thing as A=B always. Whether to gamble or not is a person choice and we should not judge people based on that. If they are happy with it and their belief, let them be.