Seems like Sun and Frank not only landed in another time, but on the other island. Which would make sense as to why the DI and Jin didn't see any plane crash.
I like that Sun is getting to be a stronger character. She was so weak at first, especially when she was letting Jin dictate her actions on the island when they first got there (she showed too much skin in the bikini and he chastized her for that, etc.)
Now she is kicking butt - buying part of her father's company, going to meet Whitmore and work with him, and then knocking Ben out (That was great!!!).
Kate could learn a thing or two from Sun right about now.
I bet Sun and Frank are the ones that go and save the others from the DI. They obviously can't be there when Ben kills the DI.