1. Find, maintaining, and keeping a high quality manufacturer in China is hard but doable.
2. Building a brand and audience is hard but doable.
3. Creating intellectual property and protecting it is hard but doable.
The folks I know who sell a lot on Amazon do all of these three things decently, and one (often more) extremely well.
From the sound of it, the folks in the article made a lame attempt at #1 and maybe a token attempt at #2 via Amazon ads.
This low level of effort simply will not cut it for most products.
I helped turn a sinking Amazon small business around last year. They did a little over $2m revenue. One of our promotions became so viral that we had $2000+ in orders with less than $20 in ad spend within a few hours. In this sense, things are always changing but I don't think it has ever been this easy to start a business with so little.
Information changes quickly so you can burn a lot of money on outdated information or pure ignorance. For example, my $2m+ client would probably have failed or were on the verge of failing because they weren't able to adapt to Amazon's increased competition in the last year. They had no idea what keyword ranking was, how to identify keywords, drive traffic, or launch products because they never needed to in the past. Because things change so quickly it is very hard to find experts who maintain their expertise... However once you understand the fundamentals, learn how to surf, riding the Amazon waters gets a lot easier.
If you can learn quickly and adapt, Amazon is still a gold mine, some risk involved, but with great payouts.