Interesting concept... Now how do we probe and test the assumption! Does the boundary of the simulation move around with us? Thus ensuring we don't reach the boundary to be able to test it in a meaningful way? Surely it would be ideal to keep the NPCs beyond immediate interaction range...
I don't think it could be proven, but it is interesting to think about this.
Definitely, I had heard simulation being advanced for a possible explanation for the blockiness of quantum, but I personally think that is just a explanation that is trying to make sense of the weirdness and counter-intuitive nature of the theory...