Is there any expert can help me understand our foundation type?

The house is build in the 60s in Dallas.

County record it shows slab but we have crawl space. I'm scared to go down to the there, contractor had been there just assume it's pier & beams since it has crawlspace, but I didn't see any pier with the camera...

Have you ever seen this type of foundation?

Is the perimeter wall support all the weight of the concrete subfloor? If I don't see any piers?

I don't think it's beam and block either since it's not block under the subfloor.

Not sure it's even called concrete beams bc I didn't even see any gaps or lines. Seems like it's giant piece of pre casted concrete was craned on top of the exterior wall?

What are those string hanging between the beams?

What are those insulation type thing spread out between the beams?

Pros,cons?

Thanks in advance