The appearance of the Zeppelin airship disrupted Shire's plan.
He had originally intended to attract the attention of the German airplanes by blowing up the reconnaissance balloon:
Blow up a reconnaissance balloon, and when a biplane appears and rushes towards another reconnaissance balloon, everyone, including the German airplanes, will think that the target is the balloon. The German airplanes will circle around the balloon to provide protection.
Then, unexpectedly, the biplane would suddenly dive and attack the "Big Bertha" on the ground...
The arrival of the Zeppelin airship made Shire realize that it might be an even more attractive target for the German pilots. When it catches fire, the explosion and flames would shock everyone. The Germans might even forget they have a strategic weapon that is more crucial to protect—the "Big Bertha."
Hence, Shire immediately redirected their target to the Zeppelin airship.
