I guess the question still is:
Is there any way to stop this backup operation that the sys.databases table thinks is still in progress?
A previous job was stopped and a job that followed that failed. It appears that SQL Server thinks the stopped job is still running. I can see no other indication of this other than ACTIVE_BACKUP_OR_RESTORE as the log_wait_reuse_desc in sys.databases. Even the location of the backup files is empty.