Citing from the paper: We refer the frequency shift satisfying the above requirements as artificial Doppler shift, implying that it has minimal impact on existing systems just like Doppler shifts caused by normal movements.

So they're just calling these "Doppler" shifts because they are so small that they don't really have any effect on the WiFi link, just like real Doppler shifts should be compensated for, while the tiny frequency shifts still contain enough information to be picked up by the BLE radio.