You must live in an outlier area. That is not the typical lingo even amongst police departments. Perhaps it is used colloquially at that department to refer to any police dog.
"Patrol Dog" is the name of a certification. Check out the United State's Police K9 Association's (A large national organization which many police departments use to certify their teams) certification requirements:
http://www.uspcak9.com/wp-content/uploads/2015/11/PATROL-DOG-I-CERTIFICATION-RULES-2016.pdf
As you can see the "Patrol Dog" certification includes a section on criminal apprehension aka bite work. The other North American k9 associations use similar terminology. Detection dogs have their own certifications that don't use that terminology.