And then Thorne said, (I'm paraphrasing, because I did not have my recorder going): "What's surprising is that the Cardinals were very good defensively in the regular season, they were tied for the National League lead with fewest errors - 75."
This is true, but silly. First, and most importantly, cumulative errors are a bad way to measure team defense. Second, the Cardinals and Diamondbacks, both of whom committed 75 errors in 2013 both committed the fourth-most errors in the game overall: the Yankees (69), Rays (59) and Orioles (54) all committed fewer. So even by Thorne's own preferred metric, the Cardinals were not close to the best in baseball at avoiding errors.
A much more accurate measure of team defense is Baseball Prospectus' Defensive Efficiency, which simply measures the frequency at which a team's defense turns batted balls into outs in which St. Louis was 21st in baseball at .703. Boston was 17th at .706. Going a step further, adjusting for context, Park Adjusted Defensive Efficiency, rates the Cardinals even worse, at -0.94, 26th in baseball. Boston is 24th.
Other advanced metrics tell a similar story. By team wide UZR, the Cardinals at -42.9 were 27th in baseball. The Sox were 10th.
By Defensive Runs Saved per 1,200 innings, the Cardinals were 26th (-3). The Sox were 15th.
The outlier is Total Zone, where per 1,200 innings, the Cardinals were league average (0 - 16th in baseball). The Sox were 12th.
The metrics disagree about Kozma specifically. By UZR/150, he was 24th among MLB SS at +8. By Total Zone, he was fourth-best in baseball at 11 runs above average. BIS' +/- puts him fifth among MLB SS.
The part that bothers me is that Thorne's line gets the story all wrong. The Cardinals were, by most full accounting systems, a poor defensive team, at best league average according to total zone. They mostly caught the balls they could reach, but their teamwide range was not strong. Thus, they committed relatively few errors while not being a strong defensive outfit. The Cardinals has strengths - they had one of the top offenses in the national league, an ace in Adam Wainwright, a young pitcher throwing like an ace in Michael Wacha, a bullpen that throws really really hard - but defense was just not one of them.