Hi. Someone already asked me this question a few months ago.
The URL does not belong to me. I don’t own it. Someone else does. The only reason why it directs back to my page is because they’re using a theme I made. And the “tumblr!daaavz” is actually a credit for the theme.
It looks like the person does not use that account anymore. Maybe you should try contacting Tumblr and ask.