Is 'Halo 5' a Microsoft in-joke?

Halo 5? Is this some kind of in-joke at Microsoft?
Halo 5? Is this some kind of in-joke at Microsoft?

A Halo 5 logo has been spotted on an Xbox 360 screen at Microsoft's Redmond, Washington offices, which begs the question: whatever happened to Halo 4?

Channel 4 News managed to spot the Halo 5 logo on a recent press visit to Microsoft HQ.