Temp drops in heavy traffic

2007 Kia Sportage just 1,500 miles on it. Manual trans.

In single digits temps for more than an hour, snowing, practically completely stalled traffic for 15 miles: near the end of the jam I noted the temp guage (which is normally is not quite halfway) start to DROP. Over the course of few minutes it dropped completely down to C. The heater stopped blowing warm air as well. No check engine or other lights go on.

After making it off highway and driving temp came back to normal range and heater was blowing warm.

I have seen a drop in temp when a cooling fan comes on on other vehicles. But usually it has to get fairly warm and it never causes it to go down all the way or the heater to stop. Ideas?

Dealer is not sure what to make of it unless it is reproducable. Things seem completely back to normal.