Not that hard. If everyone in the office had contact with someone infected then the best thing to do would have been to quarantine them all right away. Because without that, you now have the possibility that one of them had an asymptomatic case which they could have still had and given to any of the others less than a week ago, which means the others are still inside the window for being infected but not having either recovered or showed symptoms. Which means they still need to be quarantined.
This judgment call changed. If bureaucratic ineptitude was to blame, those people ignored proper procedure, making them insubordinate, and risked lives. And if they found the issue confusing enough to take eighteen days to issue the quarantine notice, they should understand why this employee might think they are being targeted for their labor practices.
The available information changed. This very quickly went from something many people weren't sure wasn't going to be maybe a nasty flu to something that has half the world staying home from work and hospitals getting overrun. Changing your procedures in response to new information is what managers should be doing.
They'd have been smarter to respond to it sooner, but better late than never.
You're trying to spin it both ways. If Amazon was just idiotic about their response to the outbreak, why did they pick that moment to suddenly take things super serious and fire the employee?