I don't work at Amazon, but our company's social media policy requires us to be transparent about a possible conflict of interest when speaking about things "close to" our company/our position in the industry and also need to be clear about whether we're speaking in an official capacity or in a personal capacity.

This is designed to reduce the chances of eager employees going out and astro-turfing or otherwise acting in trust-damaging ways while thinking they're "helping".

Crudely speaking, the fact that they work at AWS means that it’s in their best interests for AWS to be perceived positively.

When this is the case it’s often nice to state this conflict of interest, so others can take your appraisal in the appropriate context.

I’m not implying anything about the post, just stating what I assume to be the reason for the disclosure.