What “I’m interviewing someone and they don’t even know” means is he reckons he’s going to head hunt them at some point.
Of course there’s always the possibility they’ll turn the offer down. Also they do know because you get notified by linkedin whenever someone looks at your account. So they’ll see this guy continuously creeping on them and pretty much know what’s coming. The fact they haven’t reached out themselves already probably indicates they’re not interested.