I assume that he means that because of fractional reserve banking, the amount of bitcoins and bitcoin-equivalents will be much greater than 21 million.

In FRB, when you deposit money in the bank, the bank then loans out 90% of that deposit. The actual amount of money doesn't change but the perceived/effective amount of money does. The total is now 1.9 times the original amount.

Even with bitcoin, fractional reserve banking is inevitable.

Also, people are mistaken when they think that bitcoin will destroy credit cards. People like credit cards because of the security they provide. They want chargebacks. Ultimately, even if bitcoin does take off, people will use bitcoin-backed credit cards (or paypal) because they want the ability to call up the credit card company and dispute a charge.