I'm not going to say IQ per se is a dog whistle, or that there aren't sometimes benign references to it. Though even those tend to be overrated and treat it as more scientific than it really is; the 'lump of intelligence' fallacy.
But I will say I've never seen somebody in the habit of using it in an insult who wasn't also noticeably friendly with "race realists" who are obsessed with talking about IQ as one of the cornerstones of their hateful gibberish. It's a pretty reliable tell in the same neighbourhood as "boarders."
It also always makes a good moment to refer to Hawking's famous diss of IQ.
