Could I get a source on that? From what I remember, the I Am Legend creatures had more in common with ghouls or vampires than modern zombies. They weren’t at all mindless, just very aggressive and predatory. That was one of the main points of the book, which the movie completely failed to capture.
The most influential inspiration for the modern zombie is usually stated to be the 1968 Night of The Living Dead movie.
EDIT: I looked it up, and apparently Night of the Living Dead was partially inspired by I Am Legend. The fact remains though that the I Am Legend creatures only loosely resembled zombies, and it was the Night of the Living Dead that really served as the inspiration for the mindless, cannibalistic, shambling undead seen in later works.