@Shinji If you'd paid attention to the "IMPORTANT NOTICE!" at the end of the previous chapter, you'd know that Henrik is hacking Mason's mind whenever A.) they're close to each other; or B.) Mason is connected to a terminal.
Basically, Henrik is lus**** hard after Mason, and Mason's mind is catching that due to pheromones and such, and producing his "fantasies" which are actually Henrik's "fantasies" and that's why they're so super-detailed and realistic.