If you want to create a TFS query that would identify work items that have changed, but were not changed by the person working it, there is a nifty way to do this.

The filtering field can be set to <> another field that is available, but the syntax/setup in Visual Studio is not intuitive. It's in the dropdown list, but I'd never noticed it before!

AND | Changed By | <> [Field] | Assigned to  

Note that you don't include brackets on the assigned to field, and that the <> [Field] is not a placeholder for you to type the field name in, it's actually the literal command for it to parse this correctly.