My understanding is that he used to be an engineer at NVIDIA. And while I know salaries can be quite high in the US, I didn't realize they where high enough to let you spend $2 million for a 1 year hobby project.
This is an outlier. I met someone who was a millionaire working at Nvidia in 2018. That's not that uncommon working in tech. The stock has gone up about 30x since then. He's probably worth at least 20M if not more now. That's definitely an outlier.