A good post here. I too have always found the idea that Keynes's response was beyond the pale because it talked about Hayek's book very odd.
I think sometimes these one-liners develop because of famous specific pithy treatments of them.
- We all cite Hicks when we say Hayek was Keynes's main rival
- We all cite Kaldor when we say Hayek was out of his depths in the seminar
- We all cite Pigou when we say Keynes was awful to Hayek in his response
- We all cite Harrod when we say that Keynes was some kind of modern Plato that thought philosopher kings could run everything
- We all cite Hayek when we say that Hayek didn't respond to the General Theory because Keynes was so damn fickle
- We all cite Samuelson when we say that no one had a clue what Keynes was talking about
Some of these pithy treatments are stronger than others obviously. All of them come many, many years after the original events. What's unfortunate is that I think a lot of peoples' sense of intellectual history seems to come from taking each of these for granted. It gets so bad sometimes that one can get denounced (often without any kind of evidence for the purpose of actual persuasion) for even asking if we have good reason to believe one of these pithy statements - even if it's one of the pithy statements one is predisposed to agree with in broad stokes!
UPDATE: For the record I think Hicks is mostly right but probably an overstatement, Kaldor is probably relating a true event and somewhat right but overstating the extent to which it was a debacle, Pigou is wrong (and almost makes me wonder if he had seen an early draft of Keynes's General Theory and was just projecting himself on Hayek), Harrod is wrong (unless you read him just to be saying that Keynes was an elitist - which is right - but that is not how it's usually taken), Hayek is wrong, and Samuelson is wrong except perhaps for some people thoroughly unfamiliar with economics at Cambridge. These are just impressions from my reading of the thinkers, the issues, and the period. I'm not an expert, but I'm pretty decently well read and respectably published for an early career economist.