...especially with a knuckleball pitcher or a pitcher with a wicked curveball (like Greinke).
It happens less often in the majors because the catchers are so good, but in lower levels it is pretty common.
The rare aspect of this particular game is that Greinke struck out four batters in one inning. Runners reaching 1st on a dropped 3rd strike is not at all freakish or rare.
I simply think you haven't played or followed much baseball.