Can a offline database be in use?

I have a SQL Server 2014 DB where the log file filled up the disk. Since it was a test db, we decided to just delete the whole database. We took it offline, but when we try to drop it, we get a message that it cannot be dropped since it is in use. How can it be in use when it is offline? How can I get it dropped? (Preferable without taking it online.)