Did it play by looking at screenshots and sending clicks, or was there other mediation/symbolization?

It sounds like it might have been actually played in real time, which would be very important to distinguish.

I have recently seen other harnesses letting agents play real-time games in what seems like discrete time slices, turning eg Portal into something turn-based https://www.youtube.com/watch?v=ruuGXFAmiOE

There's a bot data stream already; it's probably hooked up to that rather than screencap. Yes, I believe these were playing in real time.