Yeah I'm not 100% sure how the TV rights work anymore. Are they limited in how many times they can broadcast a single team per season?Awful decision by the NFL to have this as a primetime game. Maybe they don't care as much during week one since everyone will watch anyways.
Obviously Browns @ Chiefs was projected to be (and ended up being) a far better game, but perhaps as you say NBC picked a game with two large TV markets for Week 1 and figured it was their best time to get ratings in Chicago when they're 0-0 instead of two months from now when the Bears are likely to be, say, 2-5.
SNF will still feature the Chiefs three other weeks (Chiefs @ Ravens Week 2, Bills @ Chiefs Week 5, Chiefs @ Raiders Week 10) and the Browns @ Ravens in Week 12.