Ch. 18 Q #5

Hi all, I understand Q # 5 from chapter 18 and got all the calculations right but I’m just curious about what they mean with regards to the bank’s liability. Do they mean risk? If so, how did the bank increase their risks when they gained $300,000 due to the trader’s short position? If anything, they’ve decreased their liability by that amount, no? Any thoughts would be greatly appreciated.