The police cannot, by themselves, restrict people's rights or dictate their behavior. (It might well be a good *idea* to do as they say, but that's a different matter.)There are several ways it could be true:* If there was a previous DUI/DWI and one condition of it whatever outcome, settlement, verdict, etc. was that if the man had another DUI, he would refrain from alcohal, that would be enforceable.* It's possible that that the man went before a judge as a result of this arrest, that as a condition of release, he was told he could not drink until the hearing.As you can see from the above, a judge, making some formal order or finding, would need to be involved; not just the police themselves.