Humans generally use multiple channels of communication (speech, body language, etc.), not just one, and if someone says they can't read you, that doesn't mean they aren't paying attention to what you say, it means they are paying attention to more than that, and their is a perceived incongruence between the channels of communication.

And if it is someone who has been around you a lot, it means that the usual attunement through experience that adapts this multichannel communication to the quirks of particular individuals is still insufficient to resolve the incongruence.

This can be, among other things, connected to neurodivergence and lack of experience dealing with the particular form of neurodivergence beyond one individual.