Here is the reason why feeding a snake in a separate container increases your chances of getting bit...
You have to handle/move a hungry/just fed snake into/from said separate container. This is just asking to get bit, plus chances are you have been handling rodents so your hands probably smell like a rodent to the snake.
Moving a snake to a separate container also has the potential to stress the snake which can lead to the snake refusing to eat (not that BP's really need an excuse not to eat lol)
There are only 2 reasons to feed a snake in a separate container and both can be dismissed.
1. People think that feeding a snake in its cage will make it aggressive. Simply put this is a myth with no merit what so ever most if not all big breeders feed their snake in their cages as do most of the vets here on this site. If there was an issue with doing so all of these people would stop.
A BP isn't going to associate your hand with food, especially if you use tongs to feed your snake(s). A BP uses multiple sense to determine what is and isn't food. Your hand on their own aren't going to trigger a feeding response. Most of the time when people are bit by a BP it is a defensive strike, and not a feeding strike. The difference is a defensive strike is just a bite without any coiling (constriction) where as a feeding strike involves constriction as the snake is trying to eat what it just struck at.
2. People are afraid of substrate ingestion. While this point does have some merit it too can be dismissed. A Bp can ingest some substrate without having any issues. Impaction due to substrate ingestion is extremely rare. Simply keeping an eye on the snake during feeding will keep this from becoming an issue.