This is an interesting but not surprising observation. People are genetically primed to react to face expressions, but with the underlying assumption that there is commonality in this and that one thinks that the other person shares similar feelings or reaction as oneself. It is called empathy.

With robots one sees the face but knows that there is no empathy, and that makes it creepy.

It occurs that it would be interesting to see if there was any noticeable difference in reaction between robots like this and autistic persons who, to varying degrees, have problems with relating emotionally.