Yes. If you browse to /admin and find it non-password-protected, and then deliberately use it to manipulate an application or gain access to information you reasonably know you shouldn't have access to, nobody making a prosecution decision is going to care about your nerdy protestation that there was no password.

You will be afforded the opportunity to argue that /admin was "intended to be public" in court. Depending on what you do with /admin, a judge or jury may even listen to you.