I liked to thing of him as a real-life version of Secret Agent Poyo, the ultra-badass fighting-rooster-turned-USDA-agent from the amazing comic book series Chew.
Unfortunately, the actual explanation I received from a friend for the little guy's obsession with the restaurant makes him more of a tragic character. Commercial poultry is all based around hens, and raw hen meat still gives off the hormones scents used to attract roosters who want to mate. So the lovelorn rooster keeps coming back, trying to find all the hens that his rooster-sense keeps telling him are nearby.
They're in the building behind you little buddy, but trust me you are better off not knowing the spicy, juicy, battered delicious truth.