Java/C++/Python/Ruby/Go/Perl/Scala, even Rust, are used in Amazon for various projects. What might be true is that, consider how critical your service would be, the more it is, people will lean towards to more conservative/mature/enterprise-ish languages, not exotic ones, because that inherently means risk. And Java is the go-to option under that consideration, just because, it is Java, the least controversial choice if you had asked me.
But Amazon comparing with other companies I worked with, except extremely small startup, where tech guidance is like non-existent, the least restrictive when it comes to languages. It fits the Amazon's self perception, it is pragmatic, non opinionated, moral-agnostic. It cares about customer, because customer means potential of eventual profit. However you achieved that, is not Amazon's concern.
We do actually vend a JDK. Yes, it's conservative. It's also necessary.
That said, our org did manage to have a few projects that aren't Java, so I guess I would have to concede that the Java claim is factually false as well. But it sure doesn't feel like I am empowered to choose something other than Java.
PHP is banned at Amazon, and that's the exception that proves the rule: a language being banned is so unusual that I'm aware specifically of the example of PHP.