Phone hacking?

Greetings! Haven't been on here for a while but thought this topic was worth posting about.

So my friend recently got a phone call from her friend who she is not exactly on good terms with at the moment and she has saved his contact under the swear word 'son of a b****'. But here's the weird part, he phoned her and the first thing he said was 'yeah it's son of a b****'-implying that he knows that she's saved his name as that. Bearing in mind she hasn't seen him in 6years and has no mutual friends for him to find out from someone else. So she thinks that he may have hacked her phone? But would this be possible since he hasn't actually physically got any contact with her phone (they don't live in the same country). Just wanted to know some thoughts or some other possible explanations as to how the heck he would know that? Find it so weird..