Joined WhatsApp group without admin?

Hello,
I have a strange problem.

Specifically, a member of a WhatsApp group left the group and was added back in without an admin. It's not clear how or who did it. I would also exclude the link, as the person who created the link should also be displayed.

Here is an anonymized picture (it is "Chris"):

The top two chat messages are only there for one admin. For me and the other, only the bottom message appears.

I'd be very grateful if someone could explain to me how this works or is possible. It's no longer visible in the exported chat log either.

Thanks!