USA outlet states not grounded from surge protector for all outlets in only 1 room in my house
Re-reading your post, the ground wire should be connected to the grounding screw on the outlet, not the plastic box. Plastic junction boxes don't need to be grounded (they're not metal, after all). The lack of a ground connection on the outlet itself is why the surge protector is showing an ungrounded connection, and the 3-light circuit tester would show an open ground as well.