public static bool editingTextField { get; set; }

In Editor GUI, text fields can have focus without the text being edited. For example you may switch focus between text fields or other controls by using the up and down arrow keys. Once you click inside the text field, editing of the text itself begins and the arrow keys are then used to navigate the text content. EditorGUIUtility.editingTextField is true when a text field is in this text editing mode.