I assumed that, but it's a little unclear how hard that is to do. Could they pick up the signature of a transfigured item in the pouch if they can't figure out how to get it out of the pouch? If the ring were a transfigured item, what are the odds the detection method would pick that up without a specific decision to scan the ring?

The more I think about it, the more it seems likely Hermione's body is in the pouch. The pouch has funny rules that Harry has investigated with unusual thoroughness, and he might be able to exploit that to create a situation where no one but him is likely to be able to figure out the right word to say to retrieve Hermione's body.