Reading the room is a skill. Ignoring the room and calling it confidence is not.

Noticing the mood you walked into, who is tense, what the group needs right now, takes real attention and most people never build it. Barrelling ahead regardless is easier, and it can look like self-assurance from the outside. The difference is whether you saw the room and chose, or never looked. Confidence that depends on not noticing anything is just noise with good posture.

Give yourself the first thirty seconds in any group before you say anything. Work out the energy level, who has gone quiet, what the conversation is actually about. Then join at that level rather than the one you arrived with.