Good point.
Yes 4 out of the top 6 catcher hitting teams made the playoffs, but it was also 4 of the top 13 teams made the playoffs. That's 31%. 5 of the top 17 made the playoffs. In theory, 5 out of 15 should make it, if it was randon.
Since 10 out of 30 teams make the playoffs, which is 33%, then there's not much of a correlation between having a plus hitting catching and making the playoffs. Slight, but not major.