he’s at an expensive restaurant with watson on the company dime of a wall street firm, which he hates on principle
he notices a young couple nearby, and deduces that (A) the man is about to propose to the woman and (B) they can’t normally afford to eat at a place like this
cumberbatch-sherlock would just be a dick and rattle off a bunch of deductions about them to impress watson
downey-sherlock would be an even bigger dick, march up to the couple, and tell them everything about each other that might destroy their relationship
but miller-sherlock goes and buys them the most expensive wine on the list, and charges it to the wall street firm because man, fuck wall street