its just an assumption
If Leanda joins then probably her boyfriend will too..in the picture the guy has thiw huge horned helmet, a lesser demon maybe...then we know Xander is a mage(archmage)..if the man in the picture is Xander then he could be involved in black magic judging from his looks(especially the nails
)
And there is a 6th temple..i guess that temple is dedicated to a demon deity...and they have to destroy it after they find something precius in it..
its a classic senario..but then i could be wrong