Basically, he's simulating the spice "pumpkin pie" by mixing his own. So, I'm assuming he thought it would be appropriate to add what would amount to a single measure of once spice since he's treating the spice mixture as a single spice. Does that make sense? Anyway, when I brewed my pumpkin ale, I used a whole tsp of most spices individually - Allspice, Ginger, Cinnamon, Cloves, etc. I added a whole ounce of Vanilla extract. Also, I added mine during the boil, not at flameout. From what I've read, a little heat is good to extract the spice flavors. His argument about nullifying spice flavors by cooking seems weird to me since you often bake spices at 350 deg for 45+ min when baking... Anyway, I added my spices I think at 10min. 5-10 min seems like a good time. I've tasted my wort and I can certainly guarantee that my spices aren't nullified. I think if you add what equates to 4 or spices to create 1/2 teaspoon of the mixture, for all intents and purposes using 1/8th or 1/10th of one teaspoon of each, you might as well not even bother IMO.
Also, for me, I chose to add to my pumpkin to the boil at 45 min. I steeped my specialty grains like normal and just added my pumpkin to the boil as an early-ish addition. It imparted plenty of pumpkin aroma, and gave a very nice color. I taste it in the fermented wort as well.