While it isn't true that hummingbirds are completely without a sense of smell, it isn't very well developed, and they probably have no idea what the flowers they eat nectar from smell like. While all birds have olfactory sensors of some kind, many birds tend to either not use it to any kind of advantage, or to have such an underdeveloped sense that it becomes practically useless. Lewis's sense of smell isn't too good either. This is good, as I'm not sure how much he's enjoying being covered in flowers.