The number is how many people are in front of their screens right now.
Your camera is used only to notice that a face is there and turned toward the screen. That happens on your device. No picture or video leaves it, nothing is recorded, and nobody is identified.
The only thing sent is whether you are here. Look away, hide this tab or close it, and you stop being counted.
Messages are anonymous and go to one person only. A message is erased once it has been read, unless it is reported. A cookie holds a random number so that you are counted once.