Yes, she had a permanent discharge - of what turned out to be milk!
So if yours cleared up with antibiotics, then I'm guessing you're right, it's a plain infection.
Ear infections can be fungal, with bacterial involvement, so the antibiotics clear up the latter but not the former. I have a dog that has an ongoing issue, clears up, comes back.... Grass seeds getting down the ear can trigger it too, can't see them as they get in very deep and need the vet's earscope and long fine tweezers.
So sometimes it just needs different drops and sometimes more investigation.