I started a second character and the game is starting differently. I'm following someone different through Unbound and the way it introduced looting was different. What decides this?

Probably your race.

it's who you follow into the castle (keep? i forget what they call it) when the dragon is chasing you. it's kind of dumb because i just ran into the first door i saw - you know, because a massive fucking dragon just knocked me on my arse - not exactly the best time to ask the new player to make a decision on sides

i wouldn't think it sticks though, just changes this opening. as both quests for joining the stormcloaks or imperials are still there in my quest log under misc.

At the start you either follow the Imperial dude or the Stormcloak dude. You end up at the same end point, but you fight different dudes at first.