Is it colder inside a car in winter than it is outside?

Yes it is. This is because the metal of the car conducts cold so it keeps the car as cold as it was outside the car at the coldest point. This will gradually return to the same temperature as outside when the weather heats up some. It can be - a car can be insulated enough that when the air is cold enough, temp A, it reduces the interior temperature to temp B (close but not as low as A), but sunlight and fast moving winds can blow in air warmer than both A and B: the air inside the car is not being blown away and is insulated so it doesn't go up in temp near as much as the air.