They split them so that they can abandon mobile like they have. They haven't updated their mobile apps for more than 6 months while the PC apps get updated all the time.
No that makes no sense.
In UWP, - if your app scales UI, its written in UWP compliant code, update that one app, and hey presto, it works on both devices.
With a proper UWP, there is literally zero need to "code for mobile" and this no motive to "abandon mobile". Its the same app, for all platforms - and that scalability doesn't just grant mobile, it grants xbox, IoT core, HoloLens, mixed reality and split screening.
And given this isn't a centennial port, there's no reason there (they would need to still port or switch APIs).
BTW, didn't that guy just say something has changed in one of the beta's? But your saying the mobile versions haven't changed in six months. Which is true?
Does the messenger beta app now scale or not? (It doesn't on my tablet, with the regular version, you have to manually close the friends list)
Also: Is facebook an islandwood port? Could that be the reason for feature2ing mobile, that they are still porting the ios app fully to UWP, perhaps into xamarin?
I can't fully make sense of this two versions thing yet, given the nature of UWP. It must be a partially completed port. A project in progress. Maybe they just have one guy working on it, lol, and all they need to do is right the scaling UI for it.