Those quantities don't sound enormous - nowhere near enough that being "tossed off their butts" or "very tipsy" could have been the typical experience. Four gallons of pure ethanol per year works out to 4*128/365 = 1.4 ounces per day. That would have most likely been consumed in the form of beer or cider, and even if we assume a relatively modest 5% ABV, that's only 28 fluid ounces of alcoholic beverage per day - less than two pints. That's nowhere near enough to get plastered as a regular occurrence - that's just a culture where it's normal that the beverage you consume with your meals happens to be moderately alcoholic.