In a recent mixed doubles match, my partner and I were returning serve. Our opponent hit a serve and my partner immediately called a let when she thought the ball ticked the net. The serve would have been an ace. However, it turned out the "tick" that she heard was actually our opponent's racquet scraping the ground on his service follow-through. Our opponent claimed the point should be theirs since the ball didn't actually touch the net. We thought the point should be played as a let since she honestly thought the ball ticked the net and thus she immediately called a let. Any thoughts on this?