Those cold opens are always foreshadowing, and I think your perspective here is on point.

>he seemed content at the time being Jimmy the mailroom guy,
>and decided to persue law after he saw how in awe Kim was of
>Chuck.
>So Kim rejecting him as a business partner, (and also in a way
>that she possibly thinks he's not smart enough to read between
>the lines) probably takes him back to his mail cart days, and
>how he felt watching her mingle with the grown-ups, and moving
>on from him.
>