Anyhow, going to try anyway. Original was included as part of the author's Twitter moments event series (used by some artists as an ersatz alternative to Pixiv comic collections, and Ishiyumi-sensei consistently does so for his other series too), so it was intended to be part of the comic in some capacity.
No harm trying.
Edit: As for why the author felt it appropriate to include in this series, I suppose:
This establishes the real-life origins of the story 'arc' beginning post #4535375 (Capitulum XI/Chapter 11)
It makes it unambiguous that the Zaku is equipped with an MMP-80 (the mecha 'machine gun') and a Gelgoog Shield.
The lopsided size of the MMP-80 (taken from a different scale model) adds some hilarity.
As such I placed this on Danbooru earlier because I felt the added context helps improve this story arc (as well as the comic series pool as a whole, however minor).
As for why I didn't include this in the pool earlier... er... I think I probably got confused a bit with the crossover arc on the next page, causing me to forget. Organizing two (sometimes more) different series that cross over at various points can be a little demanding.