Why domain user work as domain adminstrator?

In my company domain have one user account work as domain administrator.

When i make check for this user, i see this member in just one groupDomain User.

I try to make share for any folder and gave this user Deny for Full Control but also no use because when this account can access this folder without any limitation and can make all things also can change theowner from domain administrator to any another user. the same asAllow for Full Control.