Oh wow, mind = blown. So this happens to a single post only, and coincidentally I caught it. Ironically, by the time I posted the screenshot, which is +1 to my post count, then it had already disappeared. No one else got to see it.
LOOOOL I laughed so fucking hard at this. Basically 1337 is leet. It's a stupid hacking term used by kids. Google it.
Yes, I'm fully aware of what 1337 is, as well as all the other h4x0r language. But I couldn't make the connection because I didn't keep tabs on what my post count was.