Actually, I mis-typed. The comic says “look like” and it should be “looks like.” “Each other” is treated as singular in a case like this. "They know what each other look like is not grammatical.
Dumb, for sure… probably more dumb than boring, but for sure not funny. And all of a sudden the boring, mindless dog can talk, interact and do things for himself? Out of character.
Hence, Ralph has never “seen him.” He’s only seen him in costume.