Filler or not it happened, Also take Piccolo destroying the moon in account while he was around Raditz strength, so it does scale to Vegeta being able to do that
2. You know there's a HUGE difference between Planet and Star Level?
Yes but if you scale from Piccolo and Vegeta at the times their feats were performed it is an absolute massive difference, kind of like a ratio from a planet to a star
I can see what you mean and I commend you on that, however they've never heard of planet busting before and like I said, they had no knowledge of Vegeta's feat. DB is full of plot holes and most people know it as Piccolo shouldn't be surprised at all considering he destroyed the moon which isn't as much of a difference in size to a planet as the powers between that Piccolo and the Piccolo then is.
@animefreak1: It's Frieza though, and Zarbon as well as Vegeta, who are all planet busters (Potentially Nappa as well), and Frieza is most likely large star level, the'd have to have some impressive feats to compare to the absolute powerhouse anime known as DBZ