Um, how is this extortion?

In my opinion if i was the lender i would have done a similar thing. Because after all, logically speaking after the fork bitcoin cash + bitcoin would equal to roughly the value of 1 bitcoin before the fork. There could be a scenario where the price of bitcoin drops dramatically as a result of the fork, clearly it didn't happen this time but it is a possibility.

I'm sure that Lone Shark is financially secure enough and probably don't even care about 0.03 BTC or so.

He didn't threaten his borrowers, he simply asked them to either repay the loan or pay bitcoin cash + bitcoin, which they will get anyways.

Anyways he has waived all bitcoin cash repayments anyways, so if your agenda was really to help the borrowers then you already have seen your desired result. But i feel like you're just launching a personal vendetta on Lone Shark...