Unfortunately, Eternum being mentioned and Alex's cameo (and Moon Chi being in the Gym in the Eternum), are just nods and easter eggs and not really cannon I believe, because in MBML, Eternum isnt out yet, but in Eternum, the game has been out for a decade, so the timeline doesnt work for it to be full cannon, just nods of respect between authors. Feel free to correct me if I am wrong tho