He didn't. The father was the Nazi sympathiser, and hence the anti-semite. Eli Menkin was the guy he killed, who was Jewish (hence Jonathan said something along the lines of 'Happy Day' written at the top of a cutting of Hitler burning the Reichstag and knowing the guy we suspected he was working with was called Eli Menkin, I don't think they were working together'. Eli is very obviously a Jewish name.If her father was anti-semitic, why did he kill the secret Nazi?
The father was buried in the church with the inscription in Latin, leading Jonathan to realise that he liked using it and that the writing on the newspaper was in Latin.
And, to add to the evidence, his daughter (the old woman) said 'so my father was an anti-semite etc' to Jonathan while they were sat in the car.