Before I begin, I agree the shooter's intent was absolutely clear, and I would personally not have made this call in this situation. In friendlier games, I typically point out the rule to my opponent and ask them to be sure to call such shots in the future.
Regardless of my personal feelings, this is precisely why WSR and CSI explicitly define what is considered "not obvious":
Regardless of my personal feelings, this is precisely why WSR and CSI explicitly define what is considered "not obvious":
Obvious Shot (AR p. 77, 85) A shot in which the non-shooting player has no doubt as to, or does not question, the ball and the pocket. A shot in which the cue ball has a clear path to the object ball and the object ball has a clear path to the pocket. The following types of shots are exceptions and are defined as being "not obvious": a. bank shots; b. kick shots c. combination shots; d. shots that include caroms, kisses or cushion contacts that are not incidental; e. any shot judged as not obvious by the referee.