I, too, first heard this quote from Adam on Mythbusters as a child. But, I’m pretty sure I also heard it was said first by some philosopher.

I would later be informed that “some philosopher” was the 1984 film The Dungeon Master.

Only apparently that was not the first, and it was said in a 1974 episode of Doctor Who. Well, someone on Reddit said that, and linked to this WikiQuote page but on that page it also says it’s from The Dungeon master.

So, I don’t know what to believe any more, and I still hope it was actually an obscure lost quote of Rene Magritte or something because in my head it would just make sense.

This sounds like subtitles for a DVD commentary track, which were probably supposed to be a separate subtitle track but weren’t for some reason (or your player defaulted to them alphabetically).