YES it is an 'ambient air temp sensor'
Part of a 'cold weather kit'\
Norcold even has an OEM part number
Heat tape is wrapped around the 'weak ammonia' line to add in coolant flow during cold temp operations
Dometic doesn't have a 'cold weather' kit per se. They have a Low Ambient Temp Switch on some models that bypasses Light switch so food compartment light stays on ...provides a 'heat source' that allows for longer heating cycles/Dometic suggests turning it off above 50*F
Previous owner probably bought after market kit or Norcold Kit
Heat tape wrapped on BLUE Line