Cinnamon isn't going to kick start your fermentation or lower the gravity. When a object such as a cinnamon stick or dry hops are placed into a recently fermented beer, it will provide nucleation points and force CO2 out of solution. It might look like fermentation, but there isn't any going on... its just dissolved co2 coming out of solution. The vodka may marginally drop it, but such a small volume in the big volume of your batch isn't going to do much.
I'm guessing your fermentation wasn't complete when you took the first gravity reading. Alternatively, you could be working with a hydrometer that hasn't been calibrated and is inaccurate.