FYI the term is "guerrilla marketing" not "gorilla". I don't think he understands exactly what that means, and I really don't think QR codes count in that department.
Guerrilla marketing has to do more with creative strategies and unusual approaches that leave a lasting impression or a memorable brand experience. This usually entails reaching a large number of potential clients at a time. It's about jumping in, hitting them hard then jumping out, which is why the term comes from the phrase "Guerrilla warfare" which employs the same tactics, albeit in combat rather than marketing.
Your friend is trying to make a good case, but it falls flat. What would you have to remember in a scenario like that? The name of the band? Easy enough to find their Facebook page or site without having to scan anything. And how many people at a venue, would actually take the time to scan a code there, or even have the capability of doing so?
Statistics show that a very small number of people actually scan QR codes, even less have a QR scanner app installed on their mobile device.
They were co-opted by the marketing industry from their original purpose which was a way to organize and quickly ID auto parts by way of scanning.
Most people that use them tend to do so in a pointless manner anyway. Why would you use a QR code to link to your web site when your URL is right next to it? Although the argument is made that people can scan a vehicle when it's parked, I still don't see the value in putting them on vehicles or anything else mobile, or things that are seen while mobile, such as roadside signage etc...