I thought you were questioning butter+water on its own.
Anyway, a little digging turned up a similar technique, referred to as cooking in a butter bath:
https://www.thekitchn.com/snapshot-5-thanksgiving-vegetables-you-can-cook-in-a-butter-bath-22957555?amp=1
Now, they're using a lot more water and butter, but the concept seems to be the same. Maybe that's what the good folks at Epicurious were getting at.
Either way, the proof of the pudding is in the eating, as they say, and regardless of how they got to the plate, they were good!