This seems to have given way more weight than it should lol.
There are no technological statements behind wearing a T with a cute blue whale. It's nice, it's cool, it's blue, or simply, it might have been the next accessible piece in their wardrobe.
I think some devs need to take a serious break from emacs-vim-style warfronts. I mean, I normally don't care, but it kinda feels sad seeing tech people hitting on each other and think it is funny.
Now back to docker tech, there are people whose job is to ship containers for production, docker or whatever, who cares. It is a thing and they get paid for doing it. Obviously as part of a larger task set; DevOps, SRE, ..., the point.
I'd let them be proud of what they want. Or should I instead tell them, what you do sir is a hack, it is no real tech, don't be proud? What? Why?