It explicitly says he may not block the plate without the ball. The part you bolded about giving the catcher the right to baseline when he is fielding the ball refers to a batted play (like a dribbler up the line). Throws are not included (just like at any other position).Did you miss the other part of the rule you quoted ?
"The catcher, without the ball in his possession, has no right to block the pathway of the runner attempting to score. The base line belongs to the runner and the catcher should be there only when he is fielding a ball or when he already has the ball in his hand. "
The catcher was Clearly attempting to field the ball.
He was not fielding a ball, he was attempting to catch a throw.