I'm more impressed by the cavity PCB construction--fill with epoxy and boom dead simple waterproofing! I've never encountered this before; wonder if it's available with the batch fabs.
The technique is called "potting", and is common for small rugged devices. I think nearly all assembly houses will offer it. Some electronics components, such as relays, power converter modules also use it.
The difficult part is the step milling for the cavity. Its unusual so you need to work with the fab to get it right. Bunny Huang had a good post about it.