I doubt casinos take the time to lower the chances of a gambler winning based on their location, sometimes we hear about casinos restricting some users because they are professional gamblers or sometimes even bans are issued as the gamblers are trying to abuse the bonuses given by casinos, but I have never heard of a casino giving worst odds or lower payouts for the same bet based on their country of residence, and if this was ever found out to be true a backlash would ensue so I doubt it will ever happen.
I also don't believe the casino will make a difference in winning odds based on location or country, all winning odds will be the same for all gamblers regardless of location, so that statement is just a person's assumption because he often loses in gambling and not a fact of actual gambling, all platforms the casino targets more users from all countries that are not prohibited under the regulations of each country.
A casino platform is usually made accessible from anywhere in the world. But some country governments do not allow access to any casino platforms due to their regulations. If a casino is available from anywhere naturally they can get all kinds of advantages. In this case I have no idea about such casinos offering different benefits for a particular region. And if this kind of restriction is given then that site would definitely be under threat which would be a big loss for them.