Considering several things, like PS4's numbers in contrast to X1's, the mixed messages Halo 5 was sending before releasing (lack of offline co-op, heavily dependance on outside source material to create the story, and a not-so-great marketing campaign regarding Locke, not Chief), the massive momentum Uncharted gained with both the Uncharted Collection and ND's past endeavour (The Last of Us), in contrast to 343i's great but not Bungie great received Halo 4, and several other threads like users suggesting Splatoon beating Halo, and I find it hard to believe the idea was "unfathomable" for most people, and I'm even including some die-hard Halo fans. OP took a page on sensationalist main header from the journalism school, it seems. 
That being said, this is certainly not surprising, to me, at least. Halo has gone downhill ever since 3 in my eyes (with Reach being the biggest offender), whereas Uncharted has maintained quality throughout, aside from, ironically here, the third entry. Haven't played Halo 5 yet, but if I had to make a superficial judgment about it, I'm pretty sure it's no better than Uncharted 4.
