OoC, I think this is just another case of Male Game Developers Syndrome.
IC, it's a toughy. I can't think of any good canonical reason for Magus' Lair to have human adornments like this. But I can speculate within canon...
One possibility is that the Mystics had had a better relationship with humans in the past, and thus--especially if Magus' Lair is older rather than newer, despite the name--might have been more interested in depicting humans in their art. An evil twin possibility is that the positioning of the statues is meant to demean humans, reducing them to beasts of burden or otherwise inferior people. This possibility would not rely on better past relations between Mystics and humans. There is room for either of these possibilities since 600 AD is the earliest modern-era time period in the game. These possibilities are distinct plausible if we read the Mystics as an Arabic culture (and "Medina" appears in the literal English translation as well as the Woolsey version).
Another possibility is that there are Mystics who resemble or can resemble humans. This is a distinctly plausible possibility if we read the Mystics as the supernatural creatures of Medieval European superstition, who were always busy taking on the appearance of humans to commit un-Christian acts.
Less likely, but still possible, is that Magus' Lair is newer and the statues are of Magus' own design, and that he drew them specifically from his Zealish heritage, which features plenty of alluring female sculpture in its own right.
