I'm fully convinced he is full of shit, but if he can trade ES with even 10 sharpe (never mind 120) then 900K is chump change. Why would he spend 40+ hours a week to make some change that he doesn't need. Time is more valuable than money to a rich person.
Sadly I have only ever felt rich for very short periods of time. People have always come in to try and take it, this includes birth family, ex partners, government.
I literally have not shared my trading success or the job offer with anyone in my life and it sucks. I am just going to disappear one day if I take the offer.