Yeah, Krugman appearing on the roster surprised me too. While I haven't pored over everything he's blogged and microblogged, he hasn't sent up red flags that I recall. E.g., here he is in 2009:

Oh, Kay. Greg Mankiw looks at a graph showing that children of high-income families do better on tests, and suggests that it’s largely about inherited talent: smart people make lots of money, and also have smart kids.

But, you know, there’s lots of evidence that there’s more to it than that. For example: students with low test scores from high-income families are slightly more likely to finish college than students with high test scores from low-income families.

It’s comforting to think that we live in a meritocracy. But we don’t.

And in 2014:

There are many negative things you can say about Paul Ryan, chairman of the House Budget Committee and the G.O.P.’s de facto intellectual leader. But you have to admit that he’s a very articulate guy, an expert at sounding as if he knows what he’s talking about.

So it’s comical, in a way, to see [Paul] Ryan trying to explain away some recent remarks in which he attributed persistent poverty to a “culture, in our inner cities in particular, of men not working and just generations of men not even thinking about working.” He was, he says, simply being “inarticulate.” How could anyone suggest that it was a racial dog-whistle? Why, he even cited the work of serious scholars — people like Charles Murray, most famous for arguing that blacks are genetically inferior to whites. Oh, wait.

I suppose it's possible that he was invited to an e-mail list in the late '90s and never bothered to unsubscribe, or something like that.