When a page with a talk page (A and Talk:A, for example) is moved, only the subject page move is included in the user_editcount field. But really, all page moves should be included, not just the subject page move. Likewise, renaming a user should also increment the edit count field for every page being moved. T163966 only incremented the edit count when using Special:MovePage, but that should be done for any move in general.
See also: