Sounds like from the properties of graphene they are able to turn its thermal energy to electrical so long as the material isn't at absolute zero (obviously or then it would be a perpetual motion like machine), plus i dont see anything that says this process is lossless just high efficiency. It's definitely not perpetual motion eventually the system would lose all thermal energy and no longer output any electrical energy. If producing waste heat meant perpetual motion, geothermal would also be classified as perpetual motion, but it isn't lossless. It seems like it's essentially a heat pump at a much smaller scale where the ambient temp of the room keeps the graphene's thermal energy charged in a way. Idk nothing on this seems unintuitive unless they start trying to claim it has massive outputs. I'm guessing this is something that could help power some micro sensors by using heat in the environment but not for anything larger as you'd probably need massive sheets of graphene and they havent really said anything about scaling. Although word of caution I'm only a software engineer not a theoretical physicist, so take my ramblings with a grain of salt and defer to any actual physicists in the comments here haha