List of who 'joined' the meeting in teams meeting Chat

MauraMackinnon Hello Maura! You're not alone. It seems as if all invitees appear to have "joined the meeting" as per your description. This is a good question I don't have an answer to, but perhaps someone can explain the behavior.

To calm down the panic in your org. though you can download a meeting participant list (currently only possible during a meeting) to get an accurate attendance list.

For reference and guidance.

Download attendance reports in Teams

https://support.microsoft.com/en-us/office/download-attendance-reports-in-teams-ae7cf170-530c-47d3-84c1-3aedac74d310

Microsoft Teams meeting attendance report
https://docs.microsoft.com/en-us/microsoftteams/teams-analytics-and-reports/meeting-attendance-report 

Meeting policy settings - Meeting attendance report
https://docs.microsoft.com/en-us/microsoftteams/meeting-policies-in-teams#meeting-policy-settings---meeting-attendance-report