She commented that he had no concept of "alike or "similar". In the comprehension subtest, when asked why a policeman wore a uniform he answered "so he won't get cold".
This seems like a perfectly valid answer to the given question to me. If it wasn't the one expected, then that's probably more a reflection on the tester than the testee.
This is a common problem for testing gifted individuals, because they see things differently than expected, and that would be very likely to show up on a subtest for similarities. The test is about relationships, and different objects can be related in several different ways.