Sometimes a lender will pitch in on any per diems that you may be charged on a transaction if it goes over the initial timeframe. It sounds like your lender is or was confident that it would close on time. If he or she is willing to do this, it is definitely to your benefit.
I think that's great that the lender is willing to do this...They probably do it because many listing agents and sellers will charge the buyer $100 a day for being late. It' a common clause in many purchase agreements.