Meetup joined by non-invitee

Today I rode a meetup on Tempus Fugit - with meetup-only view - and a rider I had not invited showed up inside the meetup. They started in the pens while I started at the usual spot for meetups.

I found their ride and can see in a screenshot that their view was the same as mine. I.e. they saw me and no one else. The title of their ride was “Zwift - Group Ride: Tempus Fugit on Tempus Fugit in Watopia” - so no indication that they were doing a Meetup.

I feel like that shouldn’t be happening.

My activity has id 1174788593680384048, theirs is 1174790448544235552.