How is this an earned run?

[thedude]

I didn't see the game, but how in the world did Andrus have a fielding error on a walk? Unless I'm reading this wrong...

That is the real puzzle. Throw from catcher maybe? I looked at the box score from the game, and if memory serves. Choo was on first prior to the walk. So, I am guessing it went like this:
1) 3 balls
2) Choo off with the pitch,
3)catcher throws to second
4) ump calls pitch ball four
5) Andrus misplays the catchers throw
6) balls goes into center
7) Choo advances to third