Ezra,
Unfortunately your loan officer didn't perform his job here, which is to explain the financing. At some point you would have signed application paperwork, including a good faith estimate which would outline all fees on the loan. A proficient loan officer should have explained all of this to you. By the same token, you have to pay interest on the money if it is rolled into the loan because you did not come out of pocket at closing with the money, so it really is borrowed. Let's take the seller concession out of it, as we don't have enough info (how much your closing costs were, exactly what they were paying etc), and look at how the fees/interest work. If the closing costs total $3,000, and you signed a GFE you are agreeing to that transaction. At closing you have 2 options, bring in $3,000 to pay these fees, or roll them into the loan. The $3,000 is due at closing, if you don't have the money to bring in, or choose not to bring it in, the bank may be able to roll them into the loan but the $3,000 still has to be paid from somewhere. Since you didn't bring the funds at closing, of course you would pay interest on them, as it is money that is borrowed. Whether it is paid to the seller as money to buy the house, or to the bank to cover the fees, the lender still lent this $3,000 out. There is nothing weird about that. What is strange about this transaction is how poorly the loan officer educated you on the process, the costs, etc.
AC