Just thought I would chime in with my experience using these types of thermometers.
Yesterday I thought I would do a quick check of my grain temp before mashing and used an IR thermometer, it read 81F! My house AC was set to 72F. I checked the temp of the wall next to my thermostat and it read 72.3F, so it was accurate there. Using another thermometer I verified that the grain was 72F.
Not sure why it would read almost 10 degrees higher when pointing it at the grain. The grain was in a paper bag and had been sitting in my living room over night.