I don't think it's a calibration issue with his IR gun. It's more likely his way of measuring.
find out what the distance to spot ratio is on your IR (should say in the manual that came with it) because D/S Ratios vary greatly. Some info on that...
What is the distance to spot ratio?
D/S Ratio- Distance to Spot ratio refers to a very important feature of your infrared thermometer. This ratio is the size of the area being evaluated by the infrared thermometer as it relates to distance. In other words, the area being measured becomes larger as the distance increases. This has a profound impact on the accuracy or precision of the reading. If the target you are measuring is 6 inches in size, and your infrared thermometer has a D/S ratio of 8:1, than the maximum distance you can reliably measure the temperature of the target is 48 inches. Beyond this distance, not only is the target being measured, but whatever else falls within the "spot" is being measured as well. This means that if a very hot object is the target, and it is in cooler surroundings, than measurements taken beyond the maximum distance will include cooler elements, and lowering the "average" of what is in the "spot".
D/S Ratio X Target Size, or 8:1 X 6 = maximum measure distance of 48 inches.
As the target size decreases, or the distance to the target increases, a larger D/S Ratio becomes necessary. Using the same example above, and changing first the target size, and then the D/S ratio, you can see that this formula helps you decide the correct D/S ratio and therefore the Infrared Thermometer for your needs.
D/S Ratio X Target Size, or 8:1 X 2 = maximum measure distance of 16 inches.
D/S Ratio X Target Size, or 12:1 X 2 = maximum measure distance of 24 inches.
Hope that helps