Pete certainly wasn't "robotic." If anything, he was like fricking Gumby out there. His body bent in absolutely obscene ways on his serve ("classic" my ***), and he flailed more than he forced. I wouldn't call him "smooth" in any sense, but he sure as hell wasn't "robotic." More like "loosey goosey."
At any rate, it worked for him.
What WAS "robotic" was his strategy and execution. Serve into the corners, come in, and know that because your serve is hard, spinning like mad, and unreadable, you'll almost invariably hold. On the return, hit it hard and hope for the best. Hope that at least once per set, you can string a few lucky returns together and gather a break -- which you can do because you know you won't be broken yourself.
Simple, ruthless, effective. Very much robotic, in a sense. Even legitimately a "grind," in a sense, though the word "grinder" in the tennis lexicon has come to mean something else -- so it's an unfortunate (though accurate) choice of words in this case.