No, absolutely not. Malleus would never wear only a shirt to bed, particularly not when sharing a bed with Lilia. That would be utterly inappropriate, and he will not think on it any longer. Malleus gives Lilia another look, scandalized, when he suggests not sleeping at all.

Yes, he took it seriously.

"I will be back shortly. In the meantime, you should prepare yourself to be comfortable." Get ready for bed, in other words. Malleus turns and sweeps out of the room, as he does, to retrieve his own nighttime garments.