The evidence described does NOT generally sound like what one might find in a backdraft. Clean window glass explosion debris, and lightly singed window curtains are more evidence of the explosion flame and pressure fronts occurring before the fire.
A window frame expelled from the house with clean, intact glass panes sounds like low order damage that preceded the fire event.
Much as I am against FIBFP (fire investigation by forum posting) What you have put forward in this most recent post is more like evidence of a low order, diffuse fuel gas explosion, which was not a backdraft.
Pat Kennedy, CFEI, CFPS, MIFireE
Fire and Explosion Analyst
Sarasota, Florida
[
www.kennedy-fire.com]