Probably because it's the kind of trick that useful idiot pulls all the time, himself. He didn't really expect Eiji not to notice, just that maybe this time he'd get the hint to leave it alone. But of course that's too much to ask for.

"Then it wasn't you." And with that, Ankh walks a little further ahead in the hopes of cutting off further conversation. Eiji's going to run after him yapping like a lost puppy, but it'll buy him a few seconds.