Spotted...

I hope I haven't insulted anyone else I know by making them think I recognised them, and then giving them a different name

Nobody could possible be insulted by being called Matt, he (presumably) wouldn't think you'd forgotten his name, he'd just assume you'd "upgraded" him.

I hope he went home thinking London has suddenly become much more friendly, and decided to pass on good will to all he encountered as well.

I'm going to start using 'alright, Matt' as my greeting to everyone I know who I see on a bike now. DAS is passé and elitist anyway.

Do it often enough and you are bound to get one right eventually, even a stopped clock tells the right time twice a day.