didn't he say that 10% ago?
I believe you are correct. I also like to remind people that Peterffy didn't make his fortune predicting the direction of the market. He made it by giving all of us a tool and charging us to try and predict the direction of the market every hour of every day.
In case IBKR goes bust he can hedge it with huge amount on puts on his stock. So he does not go poorer at the end of story.