The initial basis that electrons just instrinsically have charge isn't proven. Infact there is a proof of why electrons have quantized charge (by Dirac), but it requires that magnetic monopoles exist, which haven't been observed.
I also thought it was really interesting that they chose that to start with. I personally find the electron to be one of the more confounding and least talked about pieces of the current state of physics understanding.
That being said, it is hard for me to imagine what a proof that charge is intrinsic to an electron would even look like. Proving that something is the result of something else seems much more straightforward than proving something not being the result of anything.
Also, only talking about an electron's charge being intrinsic is ignoring a lot of the mystery of it. The fact that it is a point particle is a pesky issue as well. An electron is just an electron with no underlying "pieces" or mechanisms. Obviously that could be wrong, but no one has been able to prove it yet.
I think using the electron as an example for our understanding of how the universe works is pretty ignorant. It's one of the weirdest parts of physics I've encountered during my career. It is a topic that few people actively work on but feels like their is clearly something amiss with our current understanding.
