My son is doing some work on a condo in Las Vegas. The fact
that it's a condo in a condo complex may be a clue as to how
the ceiling was constructed. (commercial codes vs. residential,
perhaps.)

The current task is to replace an old florescent fixture in the
kitchen with a much heavier hanging fixture. He removed the
old fixture to see what kind of box was used and didn't see one.
The cloth covered cable was coming right through the drywall.
He cut a hole in the drywall to see what was under it and found
this:

https://i.imgur.com/Xhwixdh.jpg

Some details, according to how my son explained the situation to
me:

The plastic tube on the cable is a piece of the old fixture, so ignore it.

He doesn't know exactly when the condo was built (he could probably
find out) but based on the use of cloth covered cable, we're thinking
maybe early 60's.

The condo complex is only one level, i.e. no living space above him.
As far as he knows there is a crawl space above the ceiling, but he
has not been able to find a way to access it so that he can see the
top of the ceiling.

The grayish paper seen on the left is not part of the drywall. It appears
to be a separate sheet of thick paper, sandwiched between the drywall
and the reddish-brown material. He said it's not stuck to the material
above it.

The reddish-brown surface is hard. When he plunged into the drywall
with his oscillating tool, it stopped plunging when it hit the material
above the drywall.

If you zoom in on the picture, it sort of looks like there may be a
round junction box buried beneath the red material, but he doesn't
want to dig any further until he has an idea of what's going on.

If the material above the drywall is some kind of fire block/retardant,
he wants to make sure that he hasn't compromised the protection - or
at least recreates it - once he figures out how to hang the new fixture.

Any ideas as to how he should proceed would be appreciated.