It is usual practice not to give a reason. If you give a reason, you are creating 'exposure' which could lead to a lawsuit, or worse, a class action lawsuit. Most big companies have this policy in place.

So no, it was not some sort of ploy to get info on your chrome extension. If they wanted to do that, they could have just unzipped it and read through your source code. It's trivial.

Lastly, kudos to Amazon for paying attention. Sounds like they investigated the vendors and banned them for review pumping.