Anyone noticed how it ominously looks a lot like Command & Conquer 3’s Tiberium and a cancelled FPS game called Tiberium? Perhaps a passing reference to it? 
Heck, even the Mantis looks like a vehicle from Tiberium:
I don’t think it’s a conspiracy, but I have a feeling that they are either paying homage to C&C and Tiberium or that they have an artist who decided to go in that same direction. Either that or it’s pure coincidence (which makes it rather funny, especially since a few developers who worked on Halo 1, 2 and 3 also worked on Tiberium).
For those who don’t believe me, here are some pictures from Tiberium:
