Maybe actually read the paper and you will find out he is quite correct:
> As shown in Section V, the electromagnetic emissions generated by the data bus are around the 2.4 GHz frequency range and overlap the Wi-Fi channels. In Wi-Fi transceiver chips, the baseband processor handles the radio, PHY and MAC layers.The Internet, transport, and application layers are processed by the software protocol stack, usually in the kernel drivers. In order to measure the interference generated, the attacker has to access the low-level radio measurement information from the PHY layer. This can be done by compromising the firmware of the Wi-Fi chips and passing the required radio measurements to the software stack
So no WiFi signals were generated. They are using the PHY to measure interference in the WiFi spectrum, and this interference is then decoded. Using your definition a microwave emits WiFi signals.