You have to love that about these sites that try to value a property. I do not know the transaction details but I can give a educated guess. The people that bought the home used 2 mortgages to finance it. The larger of the two mortgages would be recorded first so as to be the first mortgage and have highest and best claim if anything goes wrong in the future. The smaller of the two mortgages is recorded second hence the term second mortgage. The agregator site pulls legal records in the order in which they are filed so they see the last mortgage recorded, the smaller of the two, as the last transation on lien recordings. The computer system does not recognise that there are two mortgages to buy the home and shows the purchase price as the second mortgage recorded.
Result false low sale price.