To be arrested, police must have probable cause that some kind of a traffic infraction occurred. To be found guilty of DWI, the prosecutor must prove all of the elements of the crime beyond a reasonable doubt, including here, that the person was operating the vehicle. It is possible police could have arrested the individual based on a statement given by another party or if the party accused of DWI admitted to operating the vehicle.
All of that being said, the most relevant factor here is that the threshold for an arrest is simply probable cause, which is a much lower standard than proof beyond a reasonable doubt. If another party or the accused provided a statement and in that statement it was implied the accused was driving, probable cause likely is established.
The next step would be for your Criminal Defense Attorney in Buffalo NY to examine the accusatory instrument for defects and determine whether the elements could be satisfied beyond a reasonable doubt.