could be that the land is owned by the condo association. the unit owners own it so they own the land. also the association may receive a tax bill for the land. the taxes are paid because your monthly assessment includes an amount for the taxes. I also heard of cases where the unit owner receives a separate bill for the land.
ask your condo association and perhaps ask a general question about land and taxes to the assessor's office.
also, it seems a little strange that the assessed value is almost $50K more than you paid
