Regular Domain User has Admin rights on local computer, having trouble figuring out why

I'm migrating our small (40 PC) office to a domain. I've managed a domain before but I've never set one up from scratch and moved workstations over to it.

I set up ten user accounts and computers to start, and began joining them one by one. The first two went fine. The third, however, I happened to notice, doesn't prompt for the domain admin password when I want to change something. This user can even remove themselves from the domain.

It's a regular Domain User account like the others-- and with those I need to enter the Administrator password as it should be. Since I used the exact same powershell command to create all of the accounts I'm baffled why this one is suddenly different. The account is only a member of "Domain Users" (like the others), and I'm 100% sure it's logged into the domain.

One thing I should mention is that I'm using a program called the "User Profile Wizard" to migrate users' local documents. I'm not sure if that would make a difference when the local Admin account is disabled and the user is logged into the domain.

Where do I start to try and track down the issue here?