The high signal-to-noise ratio is a dead giveaway. You wouldn't get that from an accidentally scattered transmission, it requires a high-gain antenna pointed in the right direction, i.e., towards the ground.
I'd like to know how his receive antennas were pointed. In particular: if the antennas were at a very low elevation, the signals may have been pointed at another satellite near the opposite horizon. In fact, he could estimate the satellite's beamwidth by measuring how the signal strength changes as the satellite passes overhead. I'd also be interested in whether the signal seems to be pointed forward or backward (i.e. at a satellite in the same orbital plane), or to the side. (IIRC, the early optical links between Starlink satellites were forward and backward, with links between planes planned for later.)
Strong signals with broad beams pointed toward the ground to the left and right, but
not along the flight path would suggest SAR.
