My best guess, it was flying that was originally on ORD pairings.
ORD/EWR/CLE based crews regularly flowed thru IAH, but with
the huge reductions in those bases, there is no way to flow the
aircraft and crews. They rebuilt the pairings to originate in IAH.
More than likely, with the multitude of reserves elsewhere, it will
be covered by DH crews to/from IAH.