Sugar can inhibit yeast development: This is generally only an issue with sweet doughs, though. A teaspoon of yeast won't have that effect, especially if it is in a half cup of water.
But more importantly, in the times before the internet, you just couldn't reason like that. If your mother and grandmother and great-grandmother all start bread by dissolving yeast and a small amount of sugar in some water... well, you do it too. The cookbooks sometimes told you this if it wasn't too terribly old (old cookbooks expect you to know a lot, and directions get sparse).
