A Fourth Category
Krugman is actually basically right in his analysis of these three scenarios, though technically the last scenario could reflect simply optimism about profits, which is not necessarily the same thing as optimism about the economy.
However, Krugman left out a fourth category, namely the possible increase in yields combined with higher stock prices and a weaker dollar. That would be the result if inflation expectations increased while investors didn't believe that this increase in price inflation would cause the Fed to tighten policy. This is certainly a possible scenario, for example if Krugman, or someone with his views, became Fed chairman. I'll let you decide whether this was why he neglected to discuss this possibility