Ok so if ref did not double check the refs could have awarded both opening and 2nd half kickoff to Carolina
When referee Alex Kemp asked for his choice, Alexander said the Packers wanted to be on defense, which technically speaking is not the same as choosing to defer. Had Kemp not clarified, it could have cost the Packers a possession, and the Panthers would have received to start both halves.
By rule, the winner of the coin toss can choose to receive, kick off or defer the choice to the second half. With Alexander saying they wanted to be on defense, it could have been interpreted as choosing to kickoff.
It's possible the only reason Kemp double checked and asked Alexander if he meant defer was because coach Matt LaFleur makes it a point in the pregame meeting with officials to inform them of their choice should they win the toss.