Criminal Law Questions? Ask a Criminal Lawyer.
This is how they operate. That's why you need an attorney to check out the procedure. Miranda Rights are required after an arrest and before questioning. If they ask questions before an arrest or don't ask questions after the arrest then the rights do not have to be read. If they smell alcohol or it is in someone's possession and they are under 21 it doesn't matter how much they have had so a breathalyser would not be necessary.
The cops love to just arrest everyone and figure that enough of them will talk that they can build a case against everyone else.
So they can do pretty much what they like unless they are challenged by legal counsel.