return air duct?

I’m pretty sure this is a return air duct, but it seemed to be inactive. It had no filter and was being measured at 93 degrees when the the a/c was operating. All other returns were at 78. Why the three holes too?

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Was the register on an Interior or Exterior wall?

House on Slab?

How are the Ducts run?

Does there appear to be a HVAC connection to this area?

On a hallway ceiling.

Slab on grade.

No access to that part of attic.