The way I understand it in Japan it is common for official sources of comics or animation to release art, comics or short animations that aren't canon.
See the Sky Girls specials for example. They seem to take place in a parallell universe where they travel around the world to fish instead of fighting the W.O.R.M.
Similar cases are all the series that have both light novels, animes and mangas. They often differ on several details and each is only canon in their own universe. In the same way each 4koma is its own universe, separate from the canon story and often even separate from other 4komas even from the same author.
Wait, Mako, don't just...So this is Akiyama-san's roomThis is... Miporin's dakimakura ?...You didn't open the closet, did you?Full of kiss mark and strange stainsShe doesn't buy mine ?Wha ? Everyone, what are you doing here ?N, n, n, no we didn't!
