What Is Scott Sumner Thinking?

Scott Sumner replies to Larry White and says (among other things) the following:
I’d also point out that the US has experienced 3 major equity or residential real estate bubbles in periods of relatively low inflation and NGDP growth (1929, 2000, 2006) and zero major bubbles in periods with high inflation and NGDP growth (1968-81).
What is the poor guy thinking? What do the years 1929, 2000, and 2006 all have in common? If you guessed, "They are all years immediately preceding major recessions (or, in one case, the Great Depression)," you're absolutely right!

Prof. Sumner quite frequently makes statements like these in order to bait critics into having debates on his terms (read: NGDP level targeting). But I'm not going to bite. At a certain point, it just gets silly.