Probably shitty grape/apple liquor that they sweetened up with some maple syrup to make more palatable. You can brew maple sap beer, but I'm pretty sure a straight distilled liquor from the syrup is impossible. You could use it in place of white sugar in a mash and then distill that, but you would still need corn, potatoes, fruit whatever as a base and unless you're sitting on a large amount of maple syrup that you got for free it really wouldn't make any sense. Even when making the sap beer you still pasteurize and then add hops and yeast.