They did deny access into the room for a while. If they had let them in and told them "we have alcohol" would the RA not have had to call the police?
No, the RA would have never had to call the police, if they verify in anyway that there was alcohol anywhere in the room then they would have to document it and the school would deal with the matter internally. The RAs may have felt that they needed to call the police to get into the room (the owners of the room have the right to decline entry to both the RAs and the police by the way) but they should have just told the residents to cut the party now and dropped it there, you don't need to catch every single freshman that decides to drink red-handed.