I think the confusion stems from the fact that we don't really know how expensive a "request" is. Many applications can do 1000's of requests per second per machine (say 15K/sec).
Extrapolating the 15 requests per second = $370/month in the article, my hypothetical one machine application will cost $370K/month on lambda. For that, I can rent colo space, hire people to run all the services you mentioned, and gold plate the racks while I'm at it. That is crazy overhead for one machine worth of workload.
The GB*sec of a request in my extrapolated workload is certainly wrong, but I suspect a lot of people ran this calculation in their heads.
I don't really know what a request does in this context, except that version N-1 was 100x more expensive than the current one.
I think the right takeaway from the article is that spending some time to optimize workloads that are costing O(one engineer salary) to operate is often worth the effort, and, for low traffic stuff, it is hard to beat one-size-fits-all infrastructure like lambda.