The article paints two pictures:
One is that MGS is in financial trouble because their sales are well bellow expectations, even their big hitters are underperforming.
The other is that xbone and win store are failed platforms and they couldn't see those platforms making the game viable.
So, when the math was made they decided to cancel the game.
I dunno, sales target are an obvious strong reason to cancel a game, but I don't think it would be the only one. Phil himself implied when the game missed the spring showcase that he felt quality just wasn't there. The game would miss the launch date for the nTh time, and Phil also said that he wasn't too happy with the engagement figures he was reading from tests. Fable Legends was born out of a Push made by the bad Phil, one that blew in Ms' faces, and that the good phil is trying to get away from.
Of course xbox is underperforming, I don't know if the store is underperforming. It's not doing great, no argument there, but they couldn't possibly have big targets for it considering how there's little to no great content there and Tomb Raider was just the first high profile game they released, not to mention the state of the store.
I mean, Ms knew the issues the store had, there was plenty of feedback in the insider preview, they knew the store lacks features because they were already planning to add those features when the store would be merged with the xbone's, they know there was no content and they knew Tomb Raider was going to be the first high profile game, because to support AAA games on the store windows needed one update that was brought to consumers in last November. There's no way any sane reason would think that the store will sell games like hotcakes back then.
Fable Legends not meeting their expectations are a much more likely reason for its cancellation than just Ms giving up because they realized their platforms are failed just a few months ago. Sounds to me the ex employee is just looking for someone else to blame.
As for the guys you quote, i have no idea who they are, are they in a position to know what they are saying?