I would ask that they put your old cassette and chain back on the bike for free. Don't let them charge you for work or parts that you didn't ask for and didn't need. That said, be polite about. Tell your riding buddy that you think there must have been a misunderstanding and that you don't want the new parts. Hopefully, he won't give you any grief.
One of my local shops did something similar with my chain. A said I wanted a Campy Ultranarrow chain in advance of a big ride. They didnt' have one in stock and instead of calling to tell me that, they put a SRAM 10-speed chain on it. Well, my drivetrain didn't like that chain and I ended up having to get a Campy chain anyway. Because the shop had been "nice" enough do do the work at the last minute, I felt guilty complaining about it so I just sucked it up and took it to another shop. Lesson learned.
Now, I only deal with a shop that only does the work I've requested and only with the parts that I have specified. If they have any doubt or questions, they know to ask me first.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher