If the purchase of the vacant land was secured by a lien in the residence, and you are “refinancing” the residence to pay off that loan and securing your loan by the dwelling, I would report it as a refinance. HMDA gives you this option when the new loan will be secured by lien in a dwelling.
From the GIR – Code 3: Refinancing.
c. You may report all refinancings of loans secured by one-to-four-family residential dwellings, regardless of the purpose of or amount outstanding on the original loan, and regardless of the amount of new money (if any) that is for home purchase or home improvement purposes.
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The opinions expressed are mine and they are not to be taken as legal advice.