Are they interpreting it as a question of signalling without even reaching the point of evaluating it as [a propositional] statement?

That is more or less the human default. And of course you won't get them to admit it if you ask them "are you just signaling?", because that very question and its answer have signaling value themselves.

This isn't a deliberate deception; I'm convinced that most people's brains process language first and foremost as signaling-transactions and not as propositional content.