Tooth extraction, bone graft, dry socket?

I had a lower left molar extracted, and opted for a bone graft. I did everything I was instructed to do. The next day, I checked out the extraction site. I noticed a pretty big hole, pretty deep, with some suture stitched over the hole, like a basket lid (kinda). It wasn't stitched closed, and I saw no membrane or bone graft material. I didn't notice any in my mouth, ether. I went back, and as assured everything is OK. But this doesn't make sense. I'm not even sure if he really put in the graft.