Your quiet isn’t rude. Some people just mistake calm for cold.

Quiet gets read as a mood because people fill in a reason for silence, and the reason they pick is often about themselves. Being calm, slow to speak or simply not chatty is a temperament rather than a message, though it does leave room for misreading. That is not a flaw to correct. It is just worth knowing that the misreading happens.

Where it matters, give people one piece of information so they are not guessing: I am quiet today, nothing is wrong. Say it lightly and once. You do not have to become talkative to stop being misunderstood.