Eating something can definitely have an effect. Especially if I mix dairy and or the fatty deep fried greasy **** that we like to eat while drunk.
That said, the body sometimes just needs to acclimate to the new foods/drinks. If you do not eat yogurt and you start, chances are it will make you have a lot of gas and potentially irregular, but continue to eat it everyday for a week or two and it will no longer bother you (and in fact be good for you). If you do not get a lot of fiber in your diet, try getting the 25-30g of the daily recommended values, you will probably feel like it's making you go constantly and will definitely cause gas. Take that fiber for a week or two and suddenly you will go the bathroom a healthy amount (in a healthy form).
Any changes in diet may cause the body to react. With the beer, they probably only drank super filtered macro-brews, so the yeast and proteins in the homebrew might have confused their metabolism. Also beer is acidic, so large quantities of acidic liquids can make you have to go. Drink a dozen 12oz containers of orange juice and throw in a greasy sausage mcmuffin with cheese and hashbrowns (or 3) and chances are you will have the same symptoms.