The listed sugars, corn syrup and propylene glycol, are added to feed the yeast in the batch to encourage alcohol and carbon dioxide production during the fermentation of the beer. You know, to make the stuff that makes beer, beer. Yes, I'd rather drink beer that uses regular cane sugar or honey for that process, too, and would like it to be organic sugar, as well.
Why BPA, which is a carcinogen-suspect plastic when it is in contact with consumables, would be listed as an actual recipe ingredient is a bit of a stretch. Some aluminum cans are lined with plastic so that the contents will not chemically react with the metal. Tomatoes for example, are acidic, the acid reacts with steel and aluminum to produce various oxides and shit, and it makes the tomatoes taste like metal, too. To avoid that, canners have for decades used various sprayed on plastic films to protect canned foods. BPA has just been, or is about to be, banned for that use, if I recall correctly, but there would still be cans on the shelves grandfathered in. You see "BPA-Free!" everywhere on product labels for this reason.
Anyway, that site page is an amateurish mess, with zero reference citations. You would think they would want their readership to learn more about these dangerous things, but it's just a lazy, rumor-ish mess of "known fact" spewing, preaching to the choir of fellow paranoids.
