Walking-stick air-guns can be found with a faux bamboo finish, for the simple reason that the intent was for the air gun to look like a walking stick and walking sticks were often made of bamboo.
It looks to me that this strange fellow sits right between the late British pneumatics circa 1800-1850 and the Walking-stick air-guns that came to dominate after 1850. The air tank looks like it goes with a late British pneumatic. The trigger, exhaust valve assembly has the same trigger and cocking arrangement found on a walking-stick air-gun and the barrel is made to look like a walking-stick. It's only a short step from here to a full blown walking-stick air-gun.
Bet there might even be a name to be seen on the internal works, like often seen on the walking-stick air-guns.