It's not that Amazon was able to find these comments, it's that they had looked for examples, given those examples to Parler, and even that low barrier for moderation wasn't reached after a normal amount of time. As in 'here's specific examples of what you agree clearly need moderation, and are calling for terrorist attacks on our (Amazon)'s infratstructure, you (Parler) still haven't taken down days later'.

> It’s our view that this nascent plan to use volunteers to promptly identify and remove dangerous content will not work in light of the rapidly growing number of violent posts. This is further demonstrated by the fact that you still have not taken down much of the content that we’ve sent you.

They sent the examples well before they sent the final letter, gave Parler plenty of time, and Parler refused to even moderate under those extremely generous circumstances.