FWIW, Lua and AppleScript (and HyperTalk!) use(d) `--` as well.
(Edit: I think I misread “know” as “know of”; whoops.)
> I think I misread “know” as “know of”; whoops.
Don't worry about it; you didn't misread. I wasn't aware of AppleScript and HyperTalk, and though I read a bit on Lua some years ago, I either forgot or never realized that it used `--` for comments.
It's not completely unconventional. Haskell is typically styled with that kind of comma usage, too. For example,
Coincidentally, SQL and Haskell are the only languages I know that use `--` for comments.