It couldn't be further from the truth. Think about it this way:
If you feed in the home enclosure, the snake smells the rat, you dangle the rat with tongs, and then it takes the food.
If you feed outside the home enclosure, the snake smells the rat, you pick up the hungry snake and put it in an unfamiliar place, you dangle the rat and (presumably) it eats. Then you have to wait until the snake finishes eating and carefully pick up the animal who might still be hungry, and put it in the home enclosure.
Seems like option two would give your snake many more opportunities to mistake you for food than option one. If you are feeding your snake the correct amount of food per week it should never mistake you for food. You don't look or smell like a rat, so it probably won't mistake you for one on a day when the room doesn't smell like rats.
Does this make sense? Sorry, I really hate the flawed logic behind the "mistaking my hand for food" argument. It really just makes no sense. Especially for ball pythons. They are so docile!