I don’t know but I agree with your off the cuff assessment that there would be no door between house and garage. There is no entry door to the garage on the front or the side seen in some pics either. That would mean having to open the big door to get in. I think there are some pics that show the interior wall of the garage that abuts the house but I don’t recall if there was a door into the house. My memory says ‘no.’
Girlene’s post @118 of this thread shows a photo of the garage (angle so that the wall between house/garage is shown). It appears that there was some type of mudroom or sunroom addition (w/a second story porch) on that common wall. Its hard to tell if there is a door, but there would have to be some steps down from the house level to the grage.
If that were the case, I would speculate that would greatly lower the probability of the vapor/air explosion. The minute that large door opened, vapors would begin to dissipate.