You are correct, the note on the rules page is indeed wrong - it should read that we are using the BA rankings. While the rule is written incorrectly, the discussion of the rule both during creation and leading up to the draft have been consistent that we will pick an external source to use for the rankings.
While not explicit, there is a note on the rules page that implies we will be using a rankings list instead of actual MLB results
We would need to approve a source for ranking the players and a bonus price list - I suggest we try and consistently use the same source, but update our price list every 2-3 years to ensure it keeps up with MLB suggestions / averages