Wait - I see it was 35k to 40k feet. Still. INteresting.
The thing is, for me, as a controller, I would not be looking at the radar, with the intention of finding a “skin paint” aircraft, not squawking a code. I may or may not even see it, and if I did see it, without the transponder, I won’t see any information, like call sign, type aircraft and altitude. Our rules said we could give a traffic advisory, if we were not busy trying to keep other aircraft from running into each other. Our choice, to give a traffic advisory, on an unidentified aircraft, was based solely on traffic, and the decision not to give it, was not subject to question by the pilot. There is so much clutter on a radar scope, that it is almost impossible to even see an aircraft that is not squawking an SIF code.
I am unable to figure out, why any controller would be trying to figure out what a raw radar target was, and why they would be asking other aircraft if they saw it.
As I said, I was not looking for UFOs. I didn’t want to end up in a rubber room somewhere. 😀