Oda put that scene there knowing full well that everyone would jump to the conclusion that it was Sabo that needed help. It fits perfectly, right? But why make so much mystery for something that everyone is now convinced will happen? Why not just show the injured Sabo and be done with it already? Everyone is expecting him to be alive, so where's the surprise of him being revealed alive, if someone knows he's alive anyway?
But if that's a red herring, and this is actually something else that will have huge importance in a future arc, the scene still gets significance, but people will actually be surprised when everything is revealed. Maybe when we finally get to Dragon in the main story, there will be a Dragon flashback showing what happened, and we get to see something completely unexpected that leads to that scene.
I don't know what Oda intends to do with this. For simplicity's sake, I'll stand by the "dead" camp. If I'm proven wrong, I'll put a big apology in my signature, ok?
@Sammsy:
Speaking of this though, wonder what changed Iva-san. In prison he was all about not healing random pirates for no reason and here he jumps to "heal him guys" as soon as he sees a severily injured person
Because civilians and innocents are not the same as random pirates, I'd say. Almost everyone in Impel Down deserves to be there.