It's only one of the oldest tweets and/or eratta [emoji14]I don't think whirlwind attack does what you think it does. Is there a tweet or errata somewhere that states "with a separate attack roll for each target." doesn't also mean a separate damage roll for each?
If yes, I might see how whirlwind isn't a single attack with multiple attack & damage rolls, and then might be able to see how it has any bearing on what the twin spell metamagic does to the fire bolt cantrip.