You would be correct YJM... although the cow bells are legal at an outdoor contest (based on your interpretation if they can emulate game control sounds or disrupt them, or if they are used in an unsportsmanlike manor) but air horns are not legal what so ever and should have drawn a flag.
Item 7. Sportsmanship and Spectator Conduct
A. Member schools are required to conduct all of their athletic affairs in a spirit of good sportsmanship.
B. The administrators, athletic directors, and coaches of the participating schools are expected to: actively promote good sportsmanship and appropriate crowd behavior, stress the importance of demonstrating respect for the contest officials and the opposing team, and emphasize the need for proper conduct by spectators at all venues. School administrators are expected to be proactive in preventing unsportsmanlike behavior and to deal with it promptly and decisively if it occurs at the contest.
C. The coaches and athletes of the participating schools are expected to observe the highest standards of sportsmanship and ethical behavior
D. Spectator Guidelines and Conduct:
1. Drones, banners, flags, and signs are prohibited at all tournament contests. Other decorations that do not block spectator, press or team sightlines may be used with permission of and at the discretion of the Committee.
2. Streamers, confetti, and other paper debris are discouraged.
3. Sirens, horns, bells, buzzers, whistles or any other artificial or mechanical noise-making devices are strictly forbidden at all indoor events.
4. The use of any noise making device that simulates game controls devices (whistles, air horns etc.) is strictly forbidden at all contests.
5. All cheers should stress the spirit of good sportsmanship. Use only positive cheers that encourage your team. Profane, derogatory or obscene chants and taunting will not be tolerated
6. Behavior such as fans reading newspapers or turning their backs during player introductions, spectators yelling and waving their arms to distract an opponent, booing or heckling the contest officials, and being disrespectful to the opposing cheerleaders is unsportsmanlike behavior and is discouraged.
7. Face paint is permitted, but body paint is not. A shirt, top, etc. must be worn at all times.
8. Spectators must remain in the assigned seating section. Spectators are not permitted on the playing surface at any time.