while at the knees. Then it fell off the table. Happens all the time with that type of pitch.

The batter's reaction to that pitch is what got him rung up on an obvious ball. Arguing balls and strikes is a big no-no. Showing up the ump by pointing at the zone compounds the problem. I've seen umps ring up arguing batters on worse pitches.

It's possible that arguing balls and strikes had been an issue all game and the ump decided enough is enough and decided to take care of it this way rather than ejecting.

Personally, I'd have warned and then called the second pitch a ball.