I don't think it's the vodka at all. Even assuming you dumped 4 ounces of 100 proof vodka into 5 gallons, you've got 640 ounces of beer, and you added 4*50%/640, that's less than 0.33% ABV added to your beer.
But the vodka was probably 40%, it was probably less than 4 ounces, and you probably have more than 5 gallons in that 14.5 gallon fermenter. So I think it's probably more like 0.1% ABV added. If it tastes alcoholic, I think it is more likely from the 72F fermentation temp or the huge attenuation.