"Close contact is defined by CDC as someone who was within 6 feet of an infected person for a cumulative total of 15 minutes or more over a 24-hour period starting from 2 days before illness onset (or, for asymptomatic patients, 2 days prior to test specimen collection) until the time the patient is isolated."
Assuming Paige Rydberg arrived and her sample was collected on the 11th, the skaters at World Arena had intense and busy pre-nationals training sections on the 9th and 10th and cumulatively they had spent 15min within 6 ft of Paige during those two days, there's a good chance someone or even many from the World Arena would be considered a close contact/s: Tom Z, Bradie Tennell, Pooja Kalyan, Vincent Zhou, and likely more after they review security video footage at the rink. To prevent Nationals become a super spreader event, USFS has to do something and err on the safe side.