That drying was likely caused by the white fungus Sage mentioned and you missed it (easy to do as the plump oily leaves hide it some). I get rid of this very easily with milk and recommend it for over-wintering rosemary. one to ten for misting like Sage does, or if misting isn't an option you can mix the milk at three to one and apply with a cue tip on affected areas as they arise like I do (misting our big indoor rosemary in the kitchen would make my DW very unhappy, so this works best for me)
I have another smaller plant (a present!) in the breeze way where it is cold, but not freezing, and that one uses less water and never gets the mold, so that's an option too...
Hope this helps