I know there are similar questions, but I don't think they address exactly this question.
Radioactive decay is a truly random process, according to physics. We believe that there is no hidden particle or cause that we have not discovered yet that governs particle decay. On the contrary, computer generated "random" numbers follow a deterministic rule, and are not truly random.
If one did not know the rules behind computer generated "random" numbers, may believe they are truly random, since it may be very hard to understand the rule.
How can be sure that there are no yet undiscovered physical laws that would explain away the supposed randomness of the radioactive decay?