I don’t know, but one would need to thoroughly audit the code to find out one way or another. One would not draw conclusions about the non-existence of such a feature just because they’ve made exterior measurements (exterior to the black box blob of fb code) that don’t give affirmative indication. Contrarily if the technique you described did uncover such surreptitious microphone activity, that might be a bit more conclusive.

(Hard to disprove until you’ve considered all ways it could occur, and reviewed each one, and even that leaves possibilities for mistakes in method or theory)

The viewpoint is that there’s no hard evidence such behavior occurs from their code, not that it couldn’t be the case (still). Maybe some revelation will come out but I’m not betting on it. Fb is too smart for that and their official explanation makes sense.

For those that “believe”, this lesson never gets old: https://en.m.wikipedia.org/wiki/The_Thing_(listening_device) In this example, if your theory for locating a bug was based on the requirement of an electrical signal, you’d have missed such a bug entirely. Next to impossible therefore to disprove such a bug exists, if you can’t consider all of the ways in which it can exist. Hope that helps you on your mission to learn reverse engineering (a skill sadly missed in the USA throw it away culture)