No, it would not have been the 20 or so people who checked in at about the same time. It would have been the (probably) 100's of people who checked in after the infected person for *the rest of that day*.
Because there is no requirement to *check out* of a place, so the app assumes that the infected person remained in a place from the time they checked in until either 23:59 or the time they checked into a different place (if they did).
Of course, if they stayed at a place past midnight, the app would erroneously show them as not present after that time, so people who arrived after midnight would not be pinged.
Biting the hand that feeds IT
