More photos of them doing the same all over the house

Well - it isn't common for trades to cover holes. So the answer is no.

But is it acceptable? - I think so. Easy to cut, scraps are available for free. It is fire rated and does a good job at air sealing also. Have to make sure that it doesn't get wet but all of this looks very dry.

I just wouldn’t imagine dissimilar materials being used to cover up huge holes in the floor, even though that part of the floor won’t be stepped on.

I am kinda impressed that they spray foam sealed around it.

It's common for your builder and must be acceptable by the local inspector. It's being used as a "draft stop" to prevent fire spread.

Normally in a wall, the wood blocks at the top of the void also act at a draft stop or fire stop among other things. The drywall on the ceiling does the rest. In a framed void or chase, drywall is very effective for this use. The last fire job we did was missing effective draft stops in these chases and fire was able to go around the good firewalls traveling up through chases to the 2nd story attic quickly. My guess is the entire subdivision was similar.

My inspector would have required fire rated foam or caulk. What is the silver colored decking above?

That is called fireblocking, required at enclosed chases and soffits to prevent free passage of flame and combustion between floors. At this point in the job, the framing crew is long gone, the MEP rough-in has occurred, and it is ready for insulation. Usually the G.C. will go around prepping for the insulation, sometimes the insulator. It serves the same purpose as the ceiling drywall, and is the same material.

The 2 code-approved options for materials that the one doing this work would most choose from is either 1/2" drywall (for larger chases which is easy to cut with your utility knife around installed pipes) or 2x lumber (for skinny chases but should have been put in prior to MEP rough-in). Plywood is also approved, but you can imagine it is laborous cutting that around pipes. Batt insulation is also acceptable, but then you are relying more on the insulator (who are not as concerned with passing the fireblocking inspection) and they have to prevent the batts from falling down.

Note if you are wondering why the foam isn't the "fireproof stuff," it is acceptable to use a cheap foam or caulk just to make a tight seal.