This is hardly scientific but I was thinking about decomposition and remembering a dead rat on the floor of a holiday house we rented.
It was pretty much just mummified skin and bones when we arrived.
We scooped it up with a dustpan and it was past smelling, but the surprising thing was that a rat body sized hole was in the cheap nylon blend carpet and in the rubber underlay, so when we cleaned it up everything underneath had rotted away down to the cement floor.
For this reason I am doubtful that the clothes and quilt were in contact with the body as it decomposed.
Seems funny to say it, but I think the quilt is actually too well preserved to have been wrapped around a decomposing body.
This dead rat story made me laugh.
I also think, in my earlier post, that the quilt was separately deteriorated, mainly because the inner layer is very much intact/preserved.
A number of people here mentioned the pumpkin patch preserved so well because of its synthetic material, but I think it cant be only just one tiny piece is synthetic material and the rest arent. Arent there a few more pumpkin patches (should be using the same synthetic material) on the quilt but they looked so deteriorated though!