I think when it comes to random numbers, you can never prove what would be the result, provided it is implemented well.
Doubting their random number generation won't be good as they have listed the exact logic on their website here- https://magic-dice.com/provably-fair You might need some programming knowledge if you actually want to test and run it at your end.
Furthermore, you can always check the detailed logs or steps for every roll by verifying how the logic worked over here- https://magic-dice.com/verify
Hope this would help.