It's difficult for me to imagine Vito making that big of a mistake after having met Sollozzo in person, and given that Tom told the Don that the Tattaglia family were working with Sollozzo it seems like it was too big of a goof to be credible. That said, Puzo didn't make the Don infallible, and without Luca taken out of commission the story wouldn't be able to flow in the way that it did.