I've had similar experiences with HHWs; they seem to vary widely in terms of heat. One year, they were extremely mild, probably <2000shu. The next two years, they were at a Serrano++ level. Pods always looked the same, plants always produced a ton and, as I recall, all the pods from a given plant were on a very similar level...unlike, say, Jalapeños... Where you might get both burners and duds from the same plant within the same week.
I grew the HHWs for work, when I was jobcoaching at a little farm. I never really wanted to grow HHWs myself, even though I was impressed with their hardiness and productivity. Got or mild, I'm just not a big fan of their flavor. They do look rad, though.