So why is it being said to have undersold then?
I think we need to consider the source here. This is an ex-lionhead employee speaking on why his former studio was closed. And dissapointment at several MS studio's + a shrinking opportunity on Win10 is allegedly what lead to Spencer needing to present SOMETHING to the chop block.
Then we also need to consider what MS expectations might have been. I remember back in the November NPD folks were saying that MS was expecting Halo 5 to sell like Halo 3 and 4 at launch... Which seems unreasonably lofty for even a massive fan of the series, given the environment those 2 games were launching into. It's hard for me to believe that a company with the analytical resources MS has access to would bank on such projections (Quick H4 drop off, disastrous MCC launch, low xb1 installed base, lack of H3-like hype surrounding franchise). All data showed interest in Halo falling since Reach- But I suppose it's possible they were this off...
Still though, it seems like whoever is the source of this article is spreading the blame for Lionheads closure. Poor management + other underperforming studios + underperforming Win10 + expensive mediocre Lionheads game = MS needing to close SOMETHING. Lionheads was that something, yet Halo 5 gets a mention.