It was a mistake, you're still allowed to use it, it's just that they discourage people using it as the creator can easily put in a keylogger anytime they want (I highly doubt it though), so you can still continue to use it.
That post doesn't really mean anything, they've said they don't approve of the use of SK or any runecape client that isn't their own for as long as I can remember.
SK doesn't have anything that's breaking runescape rules and Jagex only disapprove of it because of any virus's that people may get from downloading 3rd party runescape clients.