That's strange- the one thing I never do if I use dry yeast if it's not rehydrated is stir. Now, dry yeast SHOULD be rehydated before using. I know some instructions say you can just sprinkle (and you can), but for the best yeast health, it should be rehydrated.
I DO aerate my wort very well, with a splashing into the fermenter, sometimes straining the wort of using a ton of hops, and then running an aquarium pump. But once that yeast touches wort, it is not stirred or shaken. The reason is this- the yeast has to rehydrate itself gradually by allowing the yeast, through osmosis, begin to acclimate to the wort.
From John Palmer's how to brew.com: Re-hydration of yeast in plain water is strongly recommended because of the principles of osmosis. In a wort with a high concentration of dissolved sugar, the water that the yeast needs cannot be drawn across the cell membrane to wet it. The water is instead locked up in the wort, hydrating the sugars. A friend of mine, who insists on remaining nameless, was misled by the term, "pitching", and for his first batch attempted to forcibly throw each granule of dried yeast into the wort so that it would be wetted. That batch didn't turn out very well.