Yeah it's a signal of "please don't come over here I'm having alone time" and if they're wagging their tail too, the tail is more of a signal to you to say "yes I'm friendly, yes I'm not considering you a threat" but combined with the eye it's "hey i see you, but please leave me a lone rn".

Also people will say "well i pet them anyway and they were happy" well yes, but it's more of a them giving up and just accepting that you're coming over and giving pets