Daniel didn't "bump" into Chang. Remember he was sitting in the jeep and was asked what he was doing he said wait any time now. Ok there he his. That's when Chang drove up. Daniel knew the exact moment Chang would arrive which tells me he knew what was going to happen as soon as he entered the others camp. He knew he was going to die. Which makes me believe it was in his journal.
So..He knew his mother "Ellie" would kill/shoot him.
Charlotte is his girlfriend that's why he told the young Charlotte to get off the island.
Is Daniel old enough to be a child on the island? Maybe we find him peaking from behind a tree to see what happened... Charlotte being his childhood friend???