Air gap... like Bluetooth?
I know what the term means, but heat is just another type of EM radiation (infra-red) that doesn't have dedicated communication hardware. The accomplishment is neat, but not useful.
As a counter-example, the paper on reading monitors from their diffuse reflected luminance is actually useful. You get a high-bandwith, air-gapped eavesdropping method. This communication by heat is more likely to be detected (as a problem, not necessarily as communication) than a steganographic (thank you) communication channel using more common EM radiation.
I'm not saying it's not 'neat'. It's just not neat and useful.