It has been suggested that it is how a protean!MitD would have known Tsukiko's ritual was only half of one (he'd have heard RC's thoughts on the matter).
MitD can see the large wooden thing on the other side of Xykon. He just doesn't seem to think that is a gate. Which makes sense if he thinks gates are wibbly-wobbly translucent holes in the fabric of reality that connect you to other planes, whereas that is a big wooden protection to stop mindless undead from frying themselves in the death arch. (this explanation is not exclusive to Protean!MitD)
GW