FW pump question

I have only used our TT's pump to winterize so am not familiar with it otherwise. However, our 1st night of our return trip from AZ was predicted to be pretty cold, so I pumped ten or so gallons into the unsanitized fresh water tank so we could flush and not have the hose freeze up. It did drop to 15F. It would only pump the prime hose water poured into the tube, so I filled a couple gallons of water from the park's spigot and just went ahead and winterized. It worked fine pulling from the antifreeze bottle.

The next day I noticed a slow drip from one of the low point drains. Could this have allowed enough air into the system to cause the pump to not pump from the FW tank?