I believe he's telling the truth. I didn't think so when they weren't finding her body. I figured he lied about that, which made me wonder about the ladder. But since they have found her, I don't doubt that is exactly where he encountered her. I think when her brother went in she was looking for another playmate, and had played there before.
One thing that is bothering me is what happened to #3 on that affidavit though. I understand in the wake of Casey Anthony LE everywhere wants to keep things to themselves to minimize jeopardizing a case. But there is something missing there that he possibly admitted to. And I'm hoping that whatever it is will be told after her autopsy. Maybe they don't want to release the rest until they confirm it.
ETA: And I DO think it is possible that SM knew the parents, or had met. At least SM and ER anyway.
Thanks for bringing that up about the #3 on the affidavit being missing. It's bothered me all day! He may have told what happened, the truth even.