Both of the rodents pictured were weaned rats, not mice, just for reference.
It isn't that one is more or less calories. They both have similar bone and meat content and all of that which would make up similar calories, but poor diet may mean lower levels of vitamins and minerals in the rats or mice which can impact the snake in the long run.
Vitamin A for example is related in most animals to skin and eye health. Lacking that could correspond in a dog to a rough coat, excessive shedding, etc. In a snake it may play a role in poor sheds or rough looking scales. (I have a theory that it may be related for some people who have snakes who shed poorly on a regular basis despite perfect husbandry and humidity for the species .. no way to really test it of course.)
A poor diet fed to the rodent could result in a feeder deficient in some nutrient(s) that over a long period of time might cause issues for the snake.
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