New user automatically join a hidden workspace

Admin invite a new user to join organization group, he joined but he automatically also join a hidden workspace without do anything.
How this happen?
He should be invited by admin to join a hidden workspace, however it did not happened in this way.
Who can tell me what’s going on?

Hi there,

Thanks for reaching out. It looks like a specific account behavior, so could you reach out directly to the support team: https://help.figma.com/hc/en-us/requests/new? They will look into it with your account information. Please make sure you use the email associated with your Figma account.

Thanks for your patience.

Toku