CMBR and neutron stars

The CMBR appears to have a perfect blackbody emission curve, at
least from what is left after passing through intergalactic and
interstellar "stuff". Normal matter does not produce the kind of
emission curve that the CMBR produces (apparently).

Certain types of neutron stars also appear to have perfect
blackbody emission curves. I'm not sure how in-general-neutral
particles can emit thermal photons, but that is another lesson.

Black holes are expected to "start with" very dense cores, such
as neutron stars.

What is the possibility that the CMBR is not "hydrogen gas at
about 3000 K" but rather the emissions of the "matter structure"
that triggered this Universe?

David A. Smith