projadd confirmation

I have used following command

projadd -c "testuser" 'user.testuser'

When I check projects -l I can see below

user.testuser:100:testuser:::

When I login to testuser and run id -p

uid=760761(testuser) gid=634152(testuser) projid=100(user.testuser)

the part I am confused when I create project I pass comment "testuser" and project name user.testuser.

After I login to testuser I can see it is using new project. I don't understand how that association happens?

Just would like to make sure testuser project will be always used by that testuser.

Also would like to confirm when user has a default project associated also all cron job