It wasn’t running on the pregnancy test then, and it’s not running on a keycap now. Both this and the pregnancy test are someone putting their own hardware into a random enclosure and saying “I’m running Doom on X!”
No, you’re not really. Would you say that I’m running Doom on a banana if I put the same hardware inside a banana peel? No, because it’s just a case for something else.
If he was running it on the keyboard’s existing processor and it had a screen in the key, like Doom on a Mac touchbar, then I would agree.