That machine is very interesting! If you own one of them, would you mind sharing how roast chamber works? I've thought a bit about how that could be done in a fully-automated fashion, but I'm curious to see what solution they came up with.
Yes, I it is probably a copper slab (they never mentioned), but there is no electrical connection, as the rest of the slides make clear: https://imgur.com/a/Rbd7e4D
It just provides a thermal connection for water cooling. The electrical connection is made through the PCB (and probably through a thick copper plate on the opposite side of the PCB)