That's how it looks! The basis is, among other things, the Building Code, and theoretically, a fine can even be imposed for non-response. The expert committee maintains a purchase price collection for its area of responsibility, where all real estate and land sales are recorded. To be able to evaluate this for the land market report, etc., it needs information about the house.
So just answer as accurately as possible, the tax office etc. has absolutely nothing to do with it. So you are not threatened there, any trouble could only arise (which is still theoretical and actually not done) if you do not respond.
Oh, and for the standard land values, by the way, sales of developed plots are pretty irrelevant; normally, only undeveloped plots and sales that are contractually sold as built for demolition are included.