I don't know if those apps mean that it is a US tablet. But I can tell you that because it is a AT&T device, that it can only be activated by AT&T. Unless you unlock it!
When you buy any phone or tab from a service provider, that provider has added their programming to that device which forbids any other provider from activating it! To change that you must unlock it.
Then you can take it a different company.
As far as changing it to a UK tab!
You may not have to, if AT&T dose business there!
Someone else may response to your post that can tell you how to determine what country that tab is from!