Ressource and contact in "Projet" maybe in other screen

When i add ressource in "Project" this add automatically contact

Only is Resource is also a contact.
It is normal !!!

Resource / User / Contact are very near things, and may represent the same person.

User : is a person that can connect to the application, getting some profile (visibility rights)
Resource : is a person (or group of person, or material) that can work on an item => be responsible, assigned to, enter work.
Contact : is a person that can be issuer. In most cases, it is a person in the customer organization, but can be internal.

So User / Resource / Contact are different roles a person can have.
So when you affect to a project a person as a resource, the person as a contact or as a user is also affected.

Moreover, the three items are stores in the same table : "user" (before V3.0) which was renamed "resource" on V3.0.