He’s training with the sick girl. That’s basically the same thing as chilling. ;3

In any case, don’t really think that Eryx and Ferrucio would’ve become battle buddies or anything. Back in the war, Ferrucio was basically just one foot soldier out of many, before eventually being brought up to be a part of the Royal Guard during the fall of the capital due to lack of many other fighting-shape individuals. He wouldn’t have been in too much of a mood to make friends either way.