A board owner has deleted the board, but I (the admin) still see it in my board list.

@Anastasia V - If you are seeing it outside of the Trash bin, then there is likely a reason for this, e.g., the a new board of the same name was created, or the board was deleted but later restored.

Who does it say owns it when you view it in your dashboard? E.g.:

What subscription type do you have? The only time a non-board owner (or co-owner) should be able to see a deleted board is when they are a Company Admin on the Enterprise Plan (more on this here). Another scenario is where the user was deleted by an admin (or they left the team on their own) and their content was assigned to another team member.