What you say is completely untrue.
Yet your description of the interrogation system is exactly what I was trying to describe, but using more "common" terms so that it's be easier to understand. Do you know WiFi at all? The interrogation code is analgous to an SSID broadcast, and the aircraft responds with a MAC. Sure, the technical terms are different, but the process isn't any different, and the results are similar. The actual RADAR is secondary now, and as you note, almost "hidden" on the displays.
Although the actual radar data hasn't been revealed, the sense of what has been shown so far is that the raw radar return, or echo, as well as the transponder Mode C, stopped simultaneously.
My understanding, such as it is, is that it was outside reflection range, and without a transponder, should be "invisible" to the commercial systems at that range. The military systems are stronger, as they don't rely on well ordered actors. But the militaries aren't stating what they saw when in public, as they want to hide their capabilities.