OBR Balk Rule history/rationale question

[Macaroo]

I checked the BRD which basically says a balk call is expected here, IF R1 is not moving to 2B. J/R states in general terms a runner must be moving for F1 to legally throw to the following base.

I don't think this is a "secret" rule, just a poorly worded AR. I guess the bottom line is that if I am the umpire I will call a balk if R1 is not stealing. When the coach becomes an umpire, he can allow it in his games. Some things, you just know.