Gmail probably considers you to be logged out of Gmail when you use the normal "Sign out" button in the upper right corner of Gmail. So indeed you are not fully connected with your Gmail account at that point. But the computer is left in a limbo state where you are still half logged-in already. All you need enter is your password. Anybody looking at your computer can see your Gmail account username.
Being in this intermediate limbo state makes it impossible for someone else to login to their Gmail account on that computer -- until you do the additional steps necessary to really, fully, logout so that Gmail on that computer doesn't think you are still there and about to login. Andy -- You received this message because you are subscribed to the Google Groups "Gmail-Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to gmail-users+unsubscr...@googlegroups.com. To post to this group, send email to gmail-users@googlegroups.com. Visit this group at https://groups.google.com/group/gmail-users. For more options, visit https://groups.google.com/d/optout.