As someone else pointed out.....they happen so infrequently, because it already requires a perfect storm of events for it to line up where it CAN happen. First, we know the SB winner has to be the home team for the season opener (except for that weird conflict in Baltimore some years back). And we know certain AFC divisions only play certain NFC divisions every 4 years. On top of that, the home/away determintation in those AFC/NFC matchups are based on who the home team was the previous matchup from 4 years ago.
So yeah, we just so happen to have a scenario in which Atlanta was scheduled to go to New England in 2017, regardless of what happened in this game. Since NE won.....why WOULDN'T that be the matchup? If Atlanta had won, you couldn't have had the SB rematch.....it would have had to be one of their home-game opponents.