I don't think the human had anything to do with why Guyver0 attacked. I admit though that some of my reasoning could be erroneous and directly contradictory to some of the facts in the manga that I can't remember rightly. The Creators put a guyver unit on their creation - a creation they controlled. The question is how they controlled it. Did the Creators just talk and expect to be obeyed, or like Alkanphel, did they have mental control over their creations? I go with that theory. Alkanphel can directly control any Zoa-form. So I believe the Creators could control their creations. So they could control the human.
Then they stuck the Guyver unit on the human. The human is probably thinking 'all is good, all is right, I'm with the Gods' but the Unit feels the mental command and interprets it as an attack and bingo, mass slaughter of everything else sent to stop it. So yep, it's a form of defence mode but I do like Adolphus' suggestion of attack instinct being the only one left. Plus I thought there was a time, just after Sho got the unit where he was unconscious. So once Guyver0 began attacking back, and the Creators couldn't maintain mental control, they thought it 'rebelled' and did everything they could to stop it. Even if they thought it was defence mode, which they might, then the Unit really should have recognised others - those on the Creators - and not attacked them but I don't think they'd have destroyed Guyver0 unless they thought they were at risk. Having a bio-engineered super-weapon that you can't control is a pretty big risk.