3DX tenant Collaboration licensing

I have a situation that two companies use 3DEXPERIENCE Cloud solution for CAD data management - each own cloud tenant - and they would like to collaborate in a way to share data through collaboration space. The question is why I can invite into my tenant a person from partner company, and I need to assign him my license if he already uses his license on his cloud tenant. The 3DX Passport is obviously the same, because username and password for login is the same. There is also a switch in member license management to select that a licencse is not "Restrict Usage to this Platform" selected?

See attached picture.