Two possibilities: Maybe you accidentally disabled barrels from the stockpile (and you can't store booze in anything else) or,
That's one good possibility. Although he's mentioned that the barracks piles are taking from "food stockpiles" (plural), another (slightly less likely) possibility is that he had tried to have two stockpiles taking from one stockpile (which can't be done), and another (which I'd hope is even less likely) is that he's accidentally got the order the wrong way round so the dwarves are being ordered to take from the barracks stockpile and put them in the main food stockpile.
If the other booze stockpile is not full, they will just continue to fill that one up until it's full, especially if its closer to the still.
Nice thought, but it's not how taking from stockpiles works. If #2 is taking from #1 then they'll keep going until #2 is full and then start filling #1
I don't know how to transfer supplies from one stockpile to another.
Press 'q' and make sure the stockpile you want things moved to is highlighted. See where you're told how many bins/barrels the stockpile has? Underneath that, it says "Take From A Pile". Press 't', then move the cursor over the stockpile you want to take from, and hit Enter. If you've done it correctly, the stockpile that's taking from another stockpile will say something like "Food Stockpile #1", indicating that it's taking stuff from the named stockpile. A stockpile can take from several different stockpiles (Pile #1 can take from piles #2 and #3) but a stockpile can only give to one stockpile (if pile #1 is taking from pile #2 and you order pile #3 to take from pile #2, your dwarves will stop taking from pile #2 and putting them into pile #1 as the newer order (i.e. #3 takes from #2) takes priority over the older order)
You don't have to know how taking from stockpiles works (I very rarely use it) but it can serve its purposes. Having huge stockpiles far away from the rest of the fort, while having much smaller stockpiles near the workshops, your crafter dwarves can go through the stuff in the smaller stockpile and haulers will refill that stockpile with stuff in the huge pile...similarly, you could have lots of large stockpiles everywhere and keep a smallish stockpile near the trade depot that takes stuff you want to trade so it's all very near to the depot when the traders arrive (few things will piss you off more than spending several minutes watching your dwarves carry stuff to the depot and just before they get the last few dregs in you get the message saying that the merchants are leaving)
I've had a similar problem in that prepared foods seem to be allowed in any food stockpile. i.e. I have one for plants only and one for unprepared fish only, and prepared foods get into both of them. There's a way to permit/forbid prepared foods? I haven't found it...
Again, press 'q' and highlight the stockpile. Press 's' to "Change Settings", go to Food and press 'u' which will permit or forbid Prepared Food (see it listed in the bottom-right of the screen?). There are a few others that work like this, the main one springing to my mind being sand bags (under the Furniture heading)