Re: How could The Offspring do this?
It's honestly a very common occurence.
Check out Sum 41, Nickleback, even Pink etc... on Youtube for other examples.
Sometimes it's coincidence (especially within the realm of pop music) and someone writes a melody/hook that sounds identical to another song. Sometimes it could be the artist ripping off someone else.
It's hard to prove, and there's not really anything you can do about it. If you're really worried, contact Hawk Nelson, make them aware of it, and suggest legal action.
Wishing I was Stanton Moore...