It means good stuff for you.
It means that the seller is willing to do owner financing, though at a somewhat high interest rate.
To translate: The seller wants you to put down $9,900. In return, the seller will offer you a loan at 10%. The loan will actually be due in 5 years, but it'll be calculated as if it were a 10 year loan. He's calculating the principle and interest at $528. It looks like the loan about would be $39,954 (approximately). Is that about right? So the total purchase price would be about $49,854.
At the end of 5 years, you'd still owe $25,206. You'd have to pay that to the seller at that point. You could do that by paying him cash, or by getting a loan for the balance. Recognize that it's quite difficult to get mortgages for that small amount, so you'd probably have to figure out some other way to repay him the remainder of the loan.
A lease-purchase would also be OK. However, buying it outright with seller financing (as you've initially described it) would be much safer for you.
Hope that helps.