I noticed the same thing, figured the heat from the smoker near by was helping the HM+rPi push the temperature up inside the enclosure. I don't have a proper enclosure yet, but when I do I plan to poke the thermistor outside of the case.
with no case & in open air, slight wind, upwind from smoker, the ambient thermistor read ~6* higher than the 62* outside temp after getting everything stabilized. Inside my lego case, it gets up to about 8* higher while inside the house. I either adjust the offset & know that it won't be right at first, or ignore it completely (it's useful for when you first get started with a new HM & calibrating probes). Mouser was out of stock when I last ordered parts, so #2 won't have it at all.