> You're implying that someone who didn't fight is presumably guilty

I can see how one could get this implication because they said "why would you" but that's a common phrase that people use to (I guess literally) call some decision into question. It's not necessarily about saying that they are obviously lying and could be more about wondering why someone would make that choice. The reply made a good case, which they don't seem to be arguing with.

Why would you use that kind of phraseology, if not to imply something?