IANAL, but deception here means, to convince someone that you're a sworn law enforcement officer, which is what a private security service would be trying to do. The exception is there so that for example an actor dressed as a police officer, or someone in a halloween costume, is not a criminal because they are not trying to convince a member of the public that they truly are a police officer.
"...for the purpose of deception" being the operative phrase. Campus "police" aren't attempting to deceive anyone, they're attempting to enforce university rules.