Not calling "Foul ball"

[NM FP Ump]

Early on in my experience I was calling a fp game where I was BU and the PU would not verbalize foul balls. Between innings I asked him if he would please verbalize them for me, and his reply was, "I give the signal for foul ball and I will verbalize the borderline foul ball, but on the routine foul balls, I just do a signal." I am a rookie, so I go along with his routine....until later in the game when a high inside pitch is swung at. The catcher puts her glove up and the ball touches her glove and goes to the backstop. Catcher moves to her left to retrieve the ball and PU puts his hands up because he lost balance when the catcher bumped into him. I tell the baserunner going from 2nd to 3rd, "it's a foul ball" and she goes back to 2nd. Well, I got my ear chewed by the OC for a foul ball call on a passed ball. I learned my lesson then and there: Call all foul balls "foul" as a PU, don't call any balls "foul" as a BU.