Another Interference?

[lds7199]

I was talking to a fellow umpire the other day and he brought up an interference question that we disagreed on. His situation goes like this:

R3 with right handed B1 at the plate. After taking an inside pitch, B1 opens up and turns his body parallel with the third base line (like taking a sign in).
F2 attempts a pickoff of the R3 at 3rd base and hits B1 with the throw.

He insists on this being interference because he believes that B1 is "making any other movement that hinders the catchers's play at home base."

So, my question is, is this play interference? If so, what makes this interference? If not, why?