Are you sure you get the whole story? Why would the female cop call for backup on a routine stop? Possible she didn't get the level of respect she expected? Some cops may take that not only as disrespect but as a sign that their counterpart may be having a loose tongue from a few too many.
After the backup was called, your friend should have known he was in deep doodoo. Now he should have understood that the cop is planning on the need of taking him to jail, needing backup for that. Last thing for your friend to do was to refuse an action that could help him
out of the situation by confirming the male cop was correct in his assessment.
This will not be an easy case to get out of, IMHO. We hear a story from your friend's perspective but they will certainly report that he was impaired and that doesn't even have to be from alc. None of the "he's good to go" will make it to the report for sure!
Of course, once the coppers have it out for someone, they will throw the book at them. The cops and the courts get paid to tango, but the citizen isn't! Now this young man is left with thousands of dollars in legal fees, time away from work and an arrest record that will stick even if the case is dismissed. He may even have to plead guilty to a lesser charge and end up with a misdemeanor on his record. Who wins???
G