Never ascribe to nefarious intent that which may be a software bug/feature.
It probably caches the first minute of hundreds of shows since those are the pain points in streaming services.
I feel like this might be it. With the Fire TV when you select to watch something it starts instantly, no matter if it is a show that you watched the previous episode or a random movie you picked out on the spot. I think it's caching everything that is visible from the homescreen, at least.
Yes this has to be a bug, I don't think they planned on downloading 80Gb/day and the bandwidth cap is not relevant. Unless they have a terrabyte HD they plan on keeping full there is no reason to download that much.
jun 7 and 8 happen to be sat & sun. so it is possible the author was browsing different shows and the tv trying to keep up with it.