Clearly, it makes a good plot device (or rather, dialog driving device) when Terminators are kind of confused when faced with human emotional phenomena. But if I think about it, it's forced and insincere in the Terminator universe. Terminators are supposed to know everything about humans to blend in, so it's kind of lame to have no idea about crying: "What's wrong with your eyes?" (T 2); not knowing about hugs: "That's a meaningless gesture" (T: Genisys)
For a Terminator, much info about humans is irrational, illogical that is just hardwired in them to get along better in a human environment. All these emotional gestures would be just additional data to be accepted as constants (to borrow a term from programming). So is there a good reason for Terminators not knowing these things?