21. Making calls on clay courts. If any part of a ball mark touches a line on a clay court, the ball shall be called good. If only part of the mark on a court can be seen, this means that the missing part is on a line or tape. A player should take a careful second look at any point-ending placement that is close to a line on a clay court. Occasionally a ball will strike the tape, jump, and then leave a full mark behind the line. This does not mean that a player is required to show an opponent the mark. The opponent shall not pass the net to inspect a mark. If a player hears the sound of a ball striking the tape and sees a clean spot on the tape near the mark, the player should give the point
to the opponent.
This is the only thing I can find, and doesn't seem to cover their initial disagreement. But since the mark can be checked and after doing so they no longer disagree then I believe the call is that the shot was out.
Völkl PB10 Mid / Pro's Pro Hi-Tec Multifiber 1.30mm @ 55lbs