edit:( I have edited the post to respond to your comment, trying to clarify what OP meant; I in no way tried to make your comment "look silly" )
Edit: you've edited your paragraph to make my reply look silly. The whole paragraph is not in O notation. In fact - the exact opposite. In the last sentence of that paragraph he shows what the expression with constant factors looks like before converting it into O notation, and it's wrong! "The product (n-1)n! is O(n × n!)." Bzzzzzzt! Wrong! He should say "The product (n-1)(n!/2) is O(n × n!)."
The median, which I don't think you're referring to, is something else (I imagine it would be substantially less than the mean).