Users not on original invite but still have access to chat

We set up a Teams meeting for training.  The only two people on the original invite are the two trainers.  If a user (internal only) wants to attend a training session, we send them a link to join.  We never add the user to the invite. 

The user joins the call and then leaves.  However, they still have access to the chat and all notifications, including when a new session starts.  We have a completely different meeting set up and send internal users a link to the meeting all the time.  On this other call, each user has temporary access to the chat.  They lose access when they leave the call.  I can't understand why we don't see the same behavior on the training teams call.

On the training meeting, how come users do not have only temporary access to the chat?  Or how can we remove users from the 'Others from chat' list?  i.e. remove from meeting altogether?  I know they can mute the chat and all that but we haven't fully rolled out Teams yet so they don't quite know this part.  Thanks,