How does the initial 50% XP bonus work with the premium rocket pass

I can confirm from my experience there is matchmaking in unranked games for sure. It's progressively ramped up harder the more I play except when I joined a party with my rookie friend where my opponents tended to match his ability more so than mine.

I like the notion that these leaderboard divisions are the key for ranked matchmaking and just like that perhaps the divisions for cumulative online stats are the key to where you go in unranked. ie Wins, Goals, Saves, etc

EDIT: Without a proper picture, it will be very difficult to guess which award you are talking about. In any case, you can view all of these awards in game from the main menu under Extras -> Stats. Scroll through all of them until you find the symbol you are talking about.

The only thing that comes to mind is this symbol (top right, bottom of the stack):

If so, that is the Playmakers Award, which is earned for every 3 assists in a single game.