A laugh can be genuine even when the joke that caused it was misunderstood.

The reaction can be real while the cause was misread. You laughed genuinely at something that was not what the speaker meant, and nothing about the feeling was false, which shows that responses are produced by what we understood rather than by what was said. Meaning happens in the receiver.

Worth knowing in both directions. When something you said lands strangely, the problem is usually in the transmission rather than in anyone’s sincerity. And when you react strongly to something, it is worth checking what you took it to mean before acting on the reaction, because you may be responding accurately to a sentence nobody spoke.