Not knowing variables in a calculation and calling something random are two different things. The fact that we can’t measure or understand those variables doesn’t really make it random.
Probability theory is just mathematics to give us a framework to make better decisions based on possible outcomes. Not only can nothing man made really be random, but you could make that point that nothing… ever… at all is random. The only way ( I know of ) that you get around it is by the existence of a soul with nothing controlling it. We make up numbers to help us understand the world. Probability theory is part of those numbers we make up. Without souls, everything we know of, a human included, is made of chemical reactions that would be quantifiable with enough information.
I probably can’t do a good job of explaining this in a short time. We’d call a coin flip random, at 50% for heads and 50% tails. If you add a little weight to one side, it might be 60% for heads and 40% for tails. (Think of loaded dice) The coin flip would still be random. The probabilities you would assign to each outcome don’t have to be even. Random and even are not the same. Random can have a different probability distribution for several events. The above scenario would have you betting heads every time. In a casino, the only bet available to you is tails.
Vegas is still a city because of them. You can say that numbers aren’t real, probability theory isn’t real, and RNGs aren’t true, but their real world applications have been demonstrated repeatedly.