He got people to withdraw over 600 million from DSB Bank in a few days, which caused the bank to run out of liquidity and forced them to freeze accounts. This meant they lost all trust in the market and needed to ask other banks for emergency financing. All other banks declined (with good reasons, a bank falling apart combined with pending legal action on the mortgage side is a very high risk for them to take).
So within three weeks DSB was bankrupt. More here: https://en.wikipedia.org/wiki/DSB_Bank
I can imaging some disgruntled customers going after Wells Fargo in the same way. They have severe legal action pending (which makes them risky for others to save) and have destroyed their image by their reactions to this (which makes it easier to motivate customers to take action). All ingredients that killed DSB are there... The only difference is that DSB was one of the smaller banks and Wells Fargo is huge.