In that Inflation paragraph above, NASA contributors addressed the CMB homogeneity as being problematic in regard to the standard cosmological view at that time. They call it a "cosmological problem", but it wasn't; it was simply a scientific observation supported by huge amounts of data. The problem was with the standard view of cosmology at that time. Either the standard cosmology had to be abandoned, or amended by adding faster-than-light expansion, dubbed Inflation, so that the background temperature could be causally connected to the Big Bang. One alternative considered must have been the existence of some external greater universe as the source of the inflowing thermalized background. The problem was that would require preconditions to the big bang, and corresponding changes to the infinitely dense zero volume nature of the singularity.