I remember as a younger man me and my mates got into skirmish coming out from a nightclub in Worcester - to cut a long story short my mate got whacked around the head with a sock full of snooker balls - police came grabbed the culprit and asked my mate if he wanted to press charges - he said no ? but in light of the CF case - it shouldn't have been an option
The test for a prosecution is two fold, is a prosecution in the public interest, and is there a realistic prospect of conviction.
The answer to the first one is usually yes, the second is more complicated.
A victim refusing to give evidence can mean there's no realistic prospect of a conviction, but there are plenty of cases where the case can proceed, as with Ms Flack.
So when the victim says I don't want it to go any further and it doesn't, that person may think their request has been listened to.
It hasn't, but if there is no prospect of a conviction without the victim's evidence, there won't be a prosecution.
The victim getting their way is an incidental consequence.
These decisions are all subjective, but due to public policy they are weighted in favour of pressing ahead if at all possible in cases of domestic violence.
In cases such as your mate's the decisions are more weighted to not going ahead.
The copper may have thought 'I possibly could build a case from other witnesses or CCTV, but it's a fairly minor assault, the victim isn't interested, so there's not much harm done by letting it go'.
Or it could have been there was obviously no case without the victim's evidence.
Most historic child abuse cases are like that, if the now adult victim doesn't want to give evidence the case is going nowhere.