The theory explains QM and gravity in a larger context, he does not necessarily have to do mathematically deduce everything and follow others interpretations. It has a solid structure and it has nuance, it is not simply just an idea thrown out there and logically it makes sense - lest you can you find the contradiction.
His theory rests on two assumptions - 1. that consciousness exists as a self-changing information system capable of evolving and 2. that evolution exists as a process of natural selection. From these assumptions, all the attributes, limitations, properties, qualities, and mechanics of consciousness – what it is, where it comes from, and how it works.
Certain things are unknowable and certain things cannot be proven to people or reproduced in an objective way in a lab setting. But he has done some experiments like this https://arxiv.org/abs/1703.00058
that show how information would get rendered to a player to achieve low computational complexity in a finite simulation.
To him, this isn't a theory, this is his real experience of reality from a very phenomenal first-hand background in out of body experiences and other reality frames.
However, to present it to the general population with no reference frame or ability to share holistically subjective experiences like that, he has to logically present it as a theory and go through the hassle of doing experiments for stuff he already knows to get the right results.