I have no idea about that 14-hour event, but otherwise what you're seeing is what I've always understood it to be;
Different events give different amounts of heat, but ALSO "decay" at different rates. Gunshots seem to be one group in your test, kinda makes sense; but torch heat, forge heat, building and mining are separate beasts.
With that in mind, for you 14 hour experience; it wouldn't be too far fetched that some heat type is just simply bugged - the xml settings for heat are perfectly unreadable, so I wouldn't be surprised if someone just misremembered the system while doing a change..
Also it used to be the case (not sure for current patch) that even jumping/landing would cause heat, which made testing .. annoying.