I've never heard of such a thing. Radar reflects off objects such as steel. If they are bouncing signals off off humans and getting a return, they are doing at a frequency I am not familiar with and neither are the Uber engineers.
Birds and raindrops give a radar return.
In 1969 Army ROTC we were shown the AN/PPS-5 Ground Surveillance Radar. It was used to detect people moving around the perimeter at night. This was a live night time demonstration. It worked.
Young folks need to work with the older ones. You'd be surprised what we know that you don't.