Thanks for the fascinating info. I have to say I was puzzled as to why the fossil has been called a mummy, when it sounded to me like an exceptionally well-preserved "normal" fossil.
It is a mummy (from what I read). It is a fossilized mummy.
That is, it was dessicated and mummified. We see this happen with animals in the right climate all the time. If the climate is right I think this happens in days, weeks or months.
Then the mummy was fossilzed. That is the original dry flesh was replaced with minerals. I guess we don't know yet if it is a total mineralization or not.
The fact that it was mummified first makes nonsense out of the "it had to happen fast" claim.