Maybe a person has read all of Bukhari. I am sure there are lots of people who have, but they may not have been increased in knowledge. They may have a knowledge of the Hadith, like as I said earlier, a knowledge of exactly how many miles it is to the sun. All knowledge is valuable. In Islam there is no knowledge which is denigrated.
Scientific knowledge is considered worthy.
Knowledge of Hadith is considered worthy. Someone may have more Knowledge from knowing a few hadith than other people from knowing all of the hadith of Bukhari. I am reminded of someone who told me that she received her Islamic education from her mother. This person was a very, very profound Muslim. She would tell us about her Hajj.