IIRC, the low assessment also reflected multiple restrictions and agreements to never develop the property and to only use it as a club. These were presumably deals Trump sought in order to minimize his property tax bill.
My belief is that 18 million regardless of it’s use is ridiculously low assessment.
What the property is worth and what it’s assessed at are obviously two different things, the judge would probably say I have only one number to go on and that’s the assessed value.