I've spawned one of these fella's in a tight space with a bunch of unarmed civilians and left him attacking for several minutes. There were no bite wounds, only lacerations (implying the LeftForearm & RightForearm attacks are taking precedent for some reason).

I have seen bitewounds on very rare occasions.

Digging through the XML, I noticed the LeftForearm & RightForearm attacks have a higher "Attack range" & "Attack damagerange" than the Head attacks (which would result in the bite/infection). Setting the values for the Head attack to the same as the LeftForearm & RightForearm attacks saw much more consistent bites.