It's an ancient meme rooted in green text brevity, intentionally misused to form another ancient meme, leading through yet another to a fourth.

Appending .exe to whatever states that the contextually implied action was performed. For example:

payday

groceries.exe

steak on sale

dinner.exe

It's being used here to obfuscate a folder, as file format was used to obfuscate distribution of the LOIC in the picture of the "It's dangerous to go alone..." meme.

But, the cake is a lie. It was Morgan Freeman, all along.

I'd like to think they were singing about something so beautiful, it can't be expressed in words, and it makes your heart ache because of it. I tell you, those voices soared higher and farther than anybody in a grey place dares to dream. It was as if some beautiful bird had flapped into our drab little cage and made these walls dissolve away.

maybe someone once performed a command like "for all files in this folder without an extension, append .exe to them" and didn't exclude subdirectories from that

no nothing similar has ever happened to me, nuh-uh, why would you ever suspect that

Well there's always self-executing archives

Why not?

Because there's nothing to prevent it.