There's some technical details that I'm not good enough to summarize, but a large gist of it seems to be that the NISTPQC seems to have gone back on it's word about being transparent through the standardization process and only ever solicited private input after round 2 and round 3 and used that non-published input to make claims about the strength of at least one contender for the standardization. And the way they've done this appears to reek of Dual EC style manipulation again from what DJB brings up? at least as far as how the process is working. I don't believe he's claiming that there's any NSA back doors but alluding to there being a private party that is steering things in ways that might not be good.
Along with also apparently some possible remarks about DJB doing something wrong also (I couldn't tell from this at least what it was. I haven't done any complete readings yet).