Yeah, what the explosion did apparrently was prevent all the events that took place that lead to the plane crash, because of that, that also undid the events of them traveling back in time which meant the explosion never happened, thus the Dharma people survived.
If that isn't confusing enough, it's made more so by Miles' contradicting theory that Jack inadvertently created the incident that started everything in the first place. Though that's really theoretically impossible, how could the plane crash on the island if it only crashed because of something the survivors did on the island which is something they only could have done if they had crashed on the island, which was caused by them after crashing on the island.
Wow, what a paradox. So that theory is out.
So if they didn't cause the incident what did?
The greatest question though is, if Jack and company successfully prevented everything from taking place, which appears to be the case because of the sideways timeline, then why are they still on the island with everything as it was? Shouldn't all that be erased from existance?
Most likely it has to do with alternate timelines, and the idea that a new future can be created, but a predeterimed one can't be erased.
But f*ck if I know, that's all I got for now.