I have known people to give a bottle of warm water after the bottle. I never did but I never heard of any trouble from doing so. If alfalfa caused stones in bucks all of my bucks over the years would have had them. They didn't. Neither did the bucks of my neighbors and they fed alfalfa to their bucks, too. Whether alfalfa causes a problem in bucks may depend on where you are and the mineral content of your water.The only time any of my bucks ever got stones was once when the automatic waterer failed and I didn't notice it until some time had passed. One of the bucklings in that pen got stones and the vet told me the lack of water was likely the cause. Made sure that didn't happen again. Some people put ACV in their buck's water to prevent stones. Don't know if it helps but it can't hurt. If your buck had stones he would most likely be straining and show signs of pain. Red urine can be caused by a number of things. There is a condition called red water in cattle but I wouldn't think he would have that. See how he is tomorrow. Is he droopy? Does he have a fever? Could he have received a blow from another goat? If that red urine continues you need to talk to your vet. See how he is tomorrow and go from there.
It is not that alfalfa *will* cause stones - it is that alfalfa has a much higher calcium content than grass hay and a diet high in calcium *can* be a cause of the development of stones. Just as how a diet high in calcium can cause serious health issues for roosters and non-laying chickens who store the excess calcium in their body vs. expelling it in the form of shelled eggs.