I was a little disappointed as well, but, it's part of the N-Line design aesthetic.
If you look at the N bumpers on the full-N cars, they are trimmed in red.
If you look at the N bumpers on the N-Line, they are trimmed in silver.
This extends to the cabin. So you get silver accents on the climate control and ignition button, but in return you get red stitching on the seats (and in Canada, red seatbelts and additional fender badges), etc.
At least the N-Line gets larger flappy paddles, too. They are easier and more comfortable to use than the nigh-vestigial size of the '18 Sport.