Ghost in the machine

We had a strange one in a Zoom meeting today - somebody joined with the user name of "-" and only appeared in the Participant List, they did not appear as a Zoom window (with video either on or off). They were able to comment to Everyone in the meeting as well.

I thought anyone joining a Zoom session would appear as a Zoom window in the Meeting window even if they had Audio and Video off or were phoning in?

Anyone else had this or knows what is happening here?

Thanks