The lack of engagement was my primary indicator, too. Since it pairs human players for the human v human matches you'd anticipate, unless they intend to deceive

The lack of engagement was my primary indicator, too. Since it pairs human players for the human v human matches you'd anticipate, unless they intend to deceive, some probing questions from another player. That's not impossible (especially if they know the "game"), but unlikely. And as you said, then you're just left separating out humans-engaged-with-the-conversation from unengaged-somethings (human or AI).