This only makes sense ONLY if Fire Type Vulpix Egg automatically becomes an ice Vulpix just because its in Alola, which doesn't make sense.
semi spoiler even though the games are technically out.
[spoil]
But judging how the only Alolan forms you can't get NORMAL are the ones that evolve from non Alolan Pokemon (especially since they use the same evolutionary method) Normal Raichu, Normal Exeggutor, Normal Marowak.
It never said you couldn't get NORMAL Vulpix or NORMAL Ninetales (by breeding)
So if true, if the egg hatches in Alola, IT SHOULD be normal Fire type Vulpix not automatically becoming Ice Type because it makes no sense, given the only reason Alolan Vulpix is a thing is because it moved to colder climates
[/spoil]
But I wouldn't past the writers to make stuff up.
Edit: On top of that, does no one really not know what the Vulpix egg looks like saying the egg looks similar or even the white version. Did you NOT see the Vulpix tail design (= two different colors) on the Pokemon egg from way back then.
And the egg Ash brought was ONLY one color, unless someone has a shot proving the egg has 2 different colors, and shows Vulpix's tail in the design.
Edit:
http://bulbapedia.bulbagarden.net/wiki/File:Vulpix_Egg.png See it has Vulpix's tail. The brown coloring part of the egg is the same though. Might mean a redesign. Though to be fair we didn't see the bottom part.