The Giants D tanked and the Giants offense was crippled.
Rams played well overall as a team but it turns out that playing well overall as a team against that Giants team meant a slaughter.
The Rams are not THAT good yet though obviously this is not criticism. It's just that slaughtering that Giants team is no indication of transcendent strength.
The game is a trap game AFTERWARDS. The potential trap being "we're THAT good!" No, wrong game to conclude that.
They are good overall but they are not 51-17 good overall, not yet.