This person was screened prior to flying out of Africa on Sept. 19, and did not develop symptoms until Sept 24. Ebola is only contagious once symptoms appear. Therefore, the people who will be evaluated are people who may have been in contact with the patient on Sept 24 and after.
According to who? The patient? If he was sick enough to go to the hospital on the 24th it's a safe bet that he was exhibiting symptoms prior to that...you know..symptoms he didn't think were serious enough to go to the hospital with.