The actual source of Flipper is a Russian company. Forming a shell company in the US doesn't change that. Sadly the Flipper team is a casualty of Putins ambitions, because they seem a good team of hackers that did a good job with their product. But the platform and software updates they provide may be susceptible to Russian gov coercion, which is I suspect the risk that many are concerned about.
[edit-to-add] that issue is orthogonal to Amazon yanking it for being a tool that could be used for potentially criminal activity. but maybe added to their decision..