Bad as in "not good", that is. That's some pretty sketchy horn playing, though they get a bit better towards the end. But that's sort of part of the charm of Beirut, Zach Condon grabs a few musicians off the street, hums the song to them while telling each part what they're supposed to do as they come in, and then they jam. It's not improvision, exactly, because everything's driven by the accordion and the singing, but it's definitely not as polished as you'd expect from your average bar band.
The band is Beirut. The song is "Nantes", off their 2007 album The Flying Club Cup.
-- Badtux the Music Penguin