The only reason (these days) that there is a limit on blood alcohol rather than absolute 0 is that you naturally have some alcohol in your blood. Even if you have never had a drink in your life you'll still have alcohol in your blood.

Some people have more then others and it has been used as a defence in Drunk in charge (DiC - very appropriate) cases where the defendent alledged that he had a peculiar liver function which produced excess alcohol.

I think he lost and was banned. Personally I wish he had been cleared and then banned from driving for life as he would always have excess alcohol in his system. Teach him for playing the system.