Oof, this sounds awful. This obviously doesn't matter now, but my understanding is that call/put options are not taxable if you exercise them[1], rather they get included in the cost basis for whatever you end up owning once you exercise. I can see your friend losing lots of money due to the price fluctuations, but hopefully he didn't pay tax he didn't owe.
I'm not a lawyer or accountant so if I'm wrong, happy to learn. :)
[1] https://www.investopedia.com/articles/active-trading/053115/...