IR thermometers will give incorrect readings when the emissivity of the surface is not close to what it's set for. Typical setting is 0.95 and many surfaces are quite far from that. Metallic/reflective surfaces especially.

My main problem wasn't that but at close range the laser dot is off position due to parallax. What I do is measure just off the board edge and get readings that are ambient for the table below. This is within 2C of the current ambient in the room usually as compared to a regular digital thermometer. Then as I move the laser near board edge with gun oriented perpendicular I can see the reading change even though the laser is off position. It jumps up for the board edge to the 40s. As I move around the board I treat the highest value I see as the ASIC temp, even though it's usually about 8mm off position. The emissivity of the chips should be quite close as I checked that black matte surfaces are close to 0.95. If I move to just off the position of the thermistor then I get a value about 2C off from the thermistor reading. For the board temp. The green board surface may not have emissivity 0.95 so that could also be why it's off from the thermistor. Or it could be it's likely around 2C off generally. The board and heat sink are barley warm to touch so I don't think they are wrong in the 40Cs, and with a 10-15C differential to the chip it seems to pull heat out adequately.

When I measure the Erupter in a similar way with no cooling I find it runs hotter. More like 65C-70C, another indication it's not too far off. If the Erupter was actually at 85C I think it would shut down. Or I hope it would, as that's likely max temp for some of the chips even if the regs typically can handle higher. I have it sitting on and making contact with a larger aluminum heat sink to help dissipate heat more than the small attached bar.