The caulifower thing is a common thing for children to do and not necessarily the result of sight words. By the time they are working on spelling lists with a word like cauliflower on it they will have already been exposed to many other long words starting with 'c' - I would assume that some event has helped that word stick in their head. For example they may have had a lengthy query discussion with a parent about why it's called a 'flower'.
Please don't compare your child to others. They are all such unique little beings. He might be able to catch a footy kicked from 50m away when another parent is struggling to get their child to catch a basketball rolled along the floor to them. Every child 'gets' things at different stages. My daughter can draw amazing pictures for her age. When I gave her a pen to play with at about 11 months, she held it in correct pencil grip and started scribbling on a box. My son is about that age now and if I give him a pen he sticks it in his mouth and crawls around the house with it! I'm going to guess that he won't be quite the artist his sister is.