Agreed. If no dwelling currently exists on the property then there can be no improvements made to a dwelling or the property on which a dwelling is located. Therefore it would not meet the definition of a home improvement loan.
Constructing a home is purchasing the home. You may be purchasing it one section at a time but you are still purchasing it. The loan (const/perm) is secured by the dwelling being constructed therefore it meets the definition of a home purchase.
The opinions expressed are mine and they are not to be taken as legal advice.