Thing is, 'oh yes' can be delivered in any number of ways in both French and english.
Pleased surprise - disappointment - a question - etc
Guessing at the context given by Jez's quoted subtitle, I think the delivery has been oh yeh? - an exchange often met with in downtown Salford prior to events turning scary. Or the similar phrase. oh aye? (yer think yer hard enough? etc being unspoken at this point)
So the translator for subtitles has tried to clarify the situation by using 'come on', which hasn't really cleared it up at all, and shows the limits of speedy translation and the real need to learn a language idiomatically and in depth in order to properly understand another culture.