...that a character I've drawn recently didn't belong to the person who I drew it for.
The fact that the character didn't belong to them wasn't mentioned; I've always asked for permission in the past to draw characters that didn't belong to me or the requester. In every case before this the fact that a character wasn't owned by either party was clear; it never occurred to me before now to bother asking to be sure beforehand.
I'm sorry for any form of pain or frustration on the owner's part that I've caused.

I've deleted the submission in question; in both anger at myself and an attempt in good faith.
I've worked with the person who requested that draw in the past, and I don't believe any ill will was intended.

I've changed my rules regarding non-personal art from now on, and they can be seen from the description on my profile page.