The quantity of photos he was taking I don't think are unfair, however, I think he should have been more aware of the noise his camera makes. On most DSLRs, the focus beep can be disabled and the amount of noise the camera makes can be reduced. Some may also offer quieter shooting modes that avoid further noise.

When attending a performance, particularly one that is largely audio based, it is impolite to make more noise than necessary. This isn't some etiquette rule that requires you to be a professional photographer to know. It's simple common sense for attending an acoustic performance. Since it is almost certain that he could have accomplished taking his photos with much less noise, I think it would have been fair to ask if he could turn off the beeping and use whatever the quietest settings for his camera were. He may, however, have not been aware of the fact he could make his camera quieter, so I'd approach it politely and try to be instructive as to how to look for focus confirmation beeps or other similar settings.