It's still an accomplishment for her, even if she's not the lead artist. Since there's nothing wrong with being proud of your fave's achievements, I really don't see why this is a problem. And this applies to any artist who succeeds through being a featured artist, not just Christina.
i don't know. it's stupid. moves like jagger was a maroon 5 song that got popular by its own merits and because of the voice, and she barely even had a real role in say something, so i don't get why they try to bring that up. it doesn't show anything important