We're seeing this galaxy as it was 280 million years after the Big Bang. But the universe didn't become transparent to photons until 100 million years after that (https://en.wikipedia.org/wiki/Recombination_(cosmology)). So that's impossible. Who's wrong, Recombination theory or this paper?

Or have I missed something?

I think you've mistaken thousands of years for millions.

As per your own link:

  Solving for z_rec gives value around 1100, which converts to a cosmic time value around 400,000 years

Doh. Thanks.

If it makes you feel any better I had the same exact reaction as you and almost posted the same thing, but managed to catch my error just in time.