Balloons were probably harder to take down than fixed wing aircraft in 1918.
I could see putting some poison chemicals in the balloon to disperse over the area if it’s shot down. That would seem to be a pretty effective weapon.
Well, it helped that the balloons were filled with hydrogen!
British developed tracer .303 in 1915. They were certainly used against Zeppelins, so I assume used against observation balloons.
I seriously doubt this balloon used hydrogen for lift.
A little phosphorus on the bullet tips set off the hydrogen real well.