get upset about it being referred to as gnu+Linux or gnu/Linux

I would say it's the opposite. Certain people get angry if you do not refer to it as GNU/Linux. These people used to be technically correct.

GNU tried to rewrite Unix from scratch under the GNU GPL license. They view their copy left license (a license where if you incorporate any code under their license, you must release the code of your project as well) as morally superior. Their kernel didn't work out, but Linus Torvolds wrote another kernel for that GNU OS.

Obviously, GNU wanted credit for the OS components that were not Linux. That's where the copypasta about "What you are using is in fact GNU+Linux..." came from. GNU is the heart of the free software movement so they have their fans as well that of course would also make that claim.

Of course, as the meme in the OP suggests, you can now have a Linux distro that either does not use code owned by GNU or uses very little of their code. I would argue Ubuntu, Arch, etc still are technically GNU+Linux as they use GNU's C compiler, their C implementation, their userspace programs like Bash and grep, etc. However, Alpine uses alternatives to GNU software such as the musl C implementation.