From this distance, while we may all have our respective sympathies, both stories are plausible and we don't really know. It is abundantly obvious that companies generally find reasons (legitimate or otherwise) to fire those advocating for a union, but it isn't exactly unheard of for an employee knowing they are facing termination or disciplinary action for legitimate reasons to cover that over with some socially-acceptable reason like various claims of discrimination or starting a union like this, etc. It's not a secret hack nobody's ever heard of.
Edit: See boiled cabbage's comment: https://news.ycombinator.com/item?id=22739059 More data can bring more clarity.
- How many employees did they quarantine in that facility?
- Were all employees exposed to the original worker quarantined?
- How long after exposure--i.e. was Smalls later, or were others quarantined at (roughly) the same time?
- Who makes the call to quarantine workers, and what discretion do they have?
I don't necessarily expect Amazon to have all those facts available immediately. I do think that they must provide them if they wish to have any credibility.