Actually, I agree with him. Indie rock can sound very alike. "Indie rock" used to refer to rock bands that were signed to independent record labels. By that definition, even the Jonas Brothers could technically become indie rock if Subpop had a temporary mental breakdown and told them "Ah, why the **** not. I'll sign ya to a contract. Besides, their mum is hot." Signing to an independent label should not be an indication of the style of music to expect from them. But that's really not the case. To most people, it just doesn't "sound" like indie rock, their fans don't dress like indie kids, and.....uh......something to do with the radio play they get.
Unfortunately, the term stopped having any meaning when people started associating a particular "sound", and style of dress, to indie rock/music. That's when you know that the term "indie rock/music" is now just a convenient way to label an overall style.
Since the term "indie" does carry certain connotations in terms of style and sound, then it's probably true that Indie Rock sounds similar in many ways, just like mainstream rock sounds similar in many ways. They sound different from each other, though.