All the viewers have the same name !

Do you have "Registration" enabled for that webinar?

If so, someone may have redistributed the webinar URL that was published with registration for you.

To avoid this, turn off "Allow panelists and attendees to join from multiple devices". This will allow only one person (device) to connect to the Webinar URL that was paid out for each individual.

Customizing webinar registration

https://support.zoom.us/hc/en-us/articles/202835649-Webinar-Registration-Customization

If the email address or name shown in the report is your staff member, the URL guidance for webinar connection may be incorrect.

Please refer to the Inviting attendees and panelists section.

https://support.zoom.us/hc/en-us/articles/200917029-Getting-started-with-Zoom-Webinars