I'm inclined to believe it was not a result of the recent head work unless something shook loose coincident with the rocker arm work, not to likely. If on the other hand, it started making the noise after replacing the head and only got worse as you put miles on it then I would suspect a plugged oil port. So that's at least some good news. You stated that it sounded really bad from the get go, so again two theories, one the guy screwed up and second is with the new pivot arm the hydraulic lash had to readjust and failed. Either way, can't see how it is your fault. BTW, where the hydraulic lash failed, how did the rockers look, were they flattened, a gnarled mess, etc. If they still looked "new" I'm inclined to believe the cam wasn't damaged.