Robert Christian married Agnes Dalzel German on 31 July 1847 - #468; bach + spinster both of the parish by licence wittnesses philip clucas pc;john quirk

In German Presentments 1847 (not filmed) - "and the sd Margaret Barr having made oath on the Holy Evangelists that Robert Christian of German is the father of the illegitimate child"

I think that solves that little mystery. - You have an interesting grandmother to Robert.