ASA 2009 Casebook Play Confusion

[SergioJ]

OK, just looked over the ASA 2009 Casebook and Play 1-57 is confusing to me. Here is what this scenario says:

OBSTRUCTION
PLAY 1-57
With no outs and R1 on 3B, B2 hits a fly ball to right field that is caught. Prior to the ball reaching F9, (a) F5 yells "go," or (b) the coach for the defense in the 3B dugout yells "go." In both cases, R1 leaves 3B too soon and the defense properly appeals.
RULING: R1 is not out. Although this is a distracting act, there is no penalty for a defensive player or a coach yelling. R1 should know their coach's voice and instruction. (1-OBSTRUCTION-B)

So, if R1 should know their coach's voice and instruction, and there is no penalty for a defensive player or a coach yelling, then why is R1 not out if defense properly appealed?

Serg