I say that based of those teams' performances during the regular split. I say it because of the overall strength of NA this year - every team save for Liquid (and P1 toward the end of the 2nd split) were capable of taking games off even the top teams. Rift Rivals even showed NA's relative strength next to EU at the time.
How am I arrogant? EU looked like it was falling to pieces. LMS wasn't looking particularly strong. Hell, 2/3rds of the LCK seeds were and still are looking a bit shaky. LPL and NA seemed to be the only two stable regions. Based off this, I was expecting TSM to make Semi Finals, or get a bad draw and go down respectably & amicably against LZ or RNG.
Clearly NA didn't deserve to end up 1st/2nd in their groups because they played abysmally in the Group Stage. Thing is, though, I never said they deserved to. I said I expected them to. I made an informed prediction based off all the things I've made note of here.