Ah, so we get to the argument of linguistic drift, and how memes affect it. Sus has another pre-existing slang use in British English, to 'suss out'. When you get down to it, most language is based off of ideas. The word 'electricity' has an etymological root in the greek word for amber (yes, the tree stuff). We might have lost the original explanation for why the ancient greeks believed amber could contain light, but it was there. I care not to delve into the reason why.
After all, the moment when people stop caring about the origin is when a meme becomes a part of common language.