I'd need to go searching for the exact wording but I think it says "around the middle of the first year" rather than 6 months. Weaning should never be at 4 months and that changed in 2003 so its been nearly 20 years since 4 months was the regular advice.
I agree that its early for waffy, I've never seen him sitting up independently so I don't think he's showing the ready signs. Some babies will though and that can be at around 5 months. I personally waited until 6 however as I said before, My girl showed all the correct signs but I was too nervous.