Have seen that presentation, but that still does not give the full context. At least, I don't think it is obvious from the video alone whether this remark was a friendly jab between friends, or whether it was a stereotypical vicious academic back-and-forth between to big names in a field.

I think this is the sequence that led to the quote.

1) People are miffed with Dijkstra due to his abrasive style.

2) John Backus has a back-and-forth with Dijkstra where he calls him arrogant.

3) The community knows of the above.

4) Dijkstra writes paper comparing Computer Science approaches in Europe vs. USA in his usual sharp style.

5) American Scientists perceive the above as dissing them and take umbrage.

6) Alan Kay writes a paper rebutting Dijkstra's paper pointing out that most of the Software is written on the American side.

7) Alan Kay then disses Dijkstra with this quote half-in-annoyance/half-tongue-in-cheek.