Same principle in that they both use electromagnetism, yes. But Qi and similar wireless charging using inductively couples coils. WISP power is generated from radio waves absorbed by the antenna generating a small current then boosted to a usable voltage for a low power microcontroller. The microcontroller can control the impedence of the antenna, changing the backscatter of the antenna, measure the change in backscatter you can get your 1s and 0s out of the sensor!

edit: wifi router could power these sensors, just a limited range.