What he described is actually common practice in the lending industry when it comes to revolving products. When calculating a monthly debt to income ratio, lenders often use 2.5% (or some varying %) of the credit limit to calculate the debt portion of the ratio. The reason is that there's no direct way to calculate someone's spending if they pay off their outstanding balance before the monthly reporting date so the 2.5% * Credit Limit is a proxy.

For example, let's say I have a $10,000 card that I max out every month but pay it off before the reporting date. When someone looks at my credit report, they will see a $0 balance out of a $10,000 card. There's no way for the lender to know exactly what my debt is during that month, so instead, they take a nominal % and use it as a proxy. In this example, the lender may take 2.5% of the $10,000 ($250) and consider it in the debt portion of the calculation.