Is a penile sore not an std in some cases? if so, in which diseases?

Sometimes: You could have a sore from trauma (e.g. Getting it caught in your zipper), a bug bite, a bacterial infection, or other less common conditions such as bechet's, reiter's syndrome and others. But a sore on the penis is an std until proven otherwise. Get it checked out. And remember that a syphilitic sore will get better on its own, but you still have syphilis.