According to the Enotes guide chapters 14-16 summary, the chimpanzee was sighted at the crowded cinema attempting to gain access to the building. This was the same cinema where the Balicki children, among other refugees, were congregated.
Bistro, the chimpanzee, had escaped from the zoo. The chimpanzee was allegedly highly intelligent and friendly, going by information about the primate that was being circulated in the dailies. After Jan heard the commotion about the chimpanzee, he slipped away from the Balicki children in attempts to find and rescue the primate. He found the chimpanzee causing havoc and scaring passengers on a British Army vehicle. Jan successfully got Bistro under control by offering the chimpanzee a cigarette, a habit that the animal picked up while at the zoo. This, in turn, earned him together with the Balicki children, dinner hosted by a British Army officer aboard the vehicle.