Nice 
Interesting, but every device that uses radio frequencies as power a source, reduce the signal strength of this signal.
If there are hundreds or thousands of sensors and devices harvesting the radio waves, then some radio stations (or who ever transits the signal) might not be happy with this.
I think it was in the 80’s where people living near a radio station could power a small light blub with an antenna.
Backscatter detection? I wonder how they are influencing the radio field.
Lots of ways to do it. They have 2 antennas so the could for instance be switching in and out a quarter wavelength transmission line between them and creating a reflection with phase shift keying. Or switching in and out a matched load or open cct to create an AM reflection.
In all honesty though they end up with data rates far below that of WiFi. If you just start out to design a conventional transmitter that goes 10x slower it will tIe about 10x less power for equivilent range.
You still need a bespoke receiver with this system.
Also note that there is nothing in this that actually harvests power. They are not mad enough to believe they cam sap useful amounts from WiFi.