IMO somebody just made that up based on it sharing the outer dimensions of the iPhone 14 which also happens to have exactly 3279 mAh. I can't really figure out what "larger battery" could mean in their release video if it isn't larger than at least the 14 if not the 16.
I can’t understand how someone can say with certainty the capacity down to a single digit (3279).
There would be manufacturing differences that would induce at least some variation from phone-to-phone.
The iPhone 16e is based on the iPhone 14 chassis, with various internal hardware components swapped out. Just like the previous iPhone SE was based on the iPhone 8. So I guess there was an assumption that maybe it uses the same battery as the 14.
But given that the cameras got swapped out for a single lens, the MagSafe magnets were removed, etc, it’s certainly conceivable that they freed up space internally for a larger battery in the 16e!