Linux 5.13 fools me?

I thought maybe it was a 5.13 thing since my other computer does not have this. It doesn't go away after installing the latest linux-libre-lts. I've been very suspicious that someone has been accessing my computers over the years. On my computers I've seen random files, that I was sure I did not put on there.

One of my other Trisquel computers crashed all the way to bios level.

What would encourage someone to put rootkits on my computers and yet at the same time do only silly things?

Very few people have noticed this easter egg; congratulations! My build script for Linux-libre does indeed contain:

export KBUILD_BUILD_TIMESTAMP="Tue Sep 27 12:35:59 EST 1983"
export KBUILD_BUILD_USER="rms"
export KBUILD_BUILD_HOST="mit-oz"

And so all all kernel versions shall report this information, as it's hardcoded in at build time.
Run: cat /proc/version to see all of it.

Thanks to prospero for picking up on the relevance for that particular date and time with GNU Project history. Those that study the raw content of the email that announced the GNU Project and have also read Free As In Freedom 2.0 will surely also pick up on the relevance of the other pieces.