It's just the rule for the credit - there is only a max of $5,000 original loan amount allowed to be used for the calculation. If you have more, you just enter $5,000. You won’t be able to use the rest as the maximum amount of the actual credit is only $500.
If you take a look at the form and follow the calculations, then you can see Line 11 mentions the $5,000 maximum directly on the form.
