External heat and internal thermal dispersion are two completely separate issues. It’s why the control panel on an oven might burn out at 200° even though it is expected to regularly endure external temperatures of 450°.
This is the “hotspot” issue that the battery article I quoted in the other thread discussed. It’s not the total amount of heat – – it’s heat in the wrong place, even very small amounts of heat.
A very common oversight is the lack of thermal analysis. In particular, for very low-power battery-operated equipment, it’s easy to think that the power levels are not high enough to worry about thermal management. However, remember that the power density of these handheld systems can actually be quite high…
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For lower power devices, with only milliwatts of internal dissipation, the end-user may not feel the unit case getting hot. However, if the dissipation in the low-power circuitry is localized to a small “hot spot” inside the unit, there may be concerns associated with device reliability or usability.
There are entire books written, and courses taught, on the engineering aspects of this issue. “Hardware is hard.” Something SmartThings knows all too well. 
