Remember there was the dynamite explosion set off by echo trying to get into the hatch just before the implosion due to the button not being pushed . When Charlie came back to camp he was disoriented and confused due to the dynamite explosion ( or so it seemed ) Charlie was already on the beach when the light etc happened from the implosion . so Echo may have also been throw clear before the hatch happening do to the dynamite explosion . Just a thought .....