In the old hardware terminals, and current terminal emulators, ^H (or CTRL+h) is "Backspace signal". It has the effect of pressing backspace.

So, ^H^H^H means "delete three characters, excluding '^H's". Like the person typing the comment changes their mind and deletes the characters (or the word) before writing else.

It's an stylized way of euphemism. i.e.: Actually I want to say this, but I substitute it for that.