Nowhere in that text does it say “managers are the real software architects”. What it does say is “what managers do affects software architecture”. Sure you can extrapolate that to delusions of grandeur, but if you take into account the explicit call for collaboration it is much more likely what was meant is more along the lines of “we can mess things up if we ignore the architecture, so let’s talk to the real software architects before making org decisions”.
About the comic: That one does have the line “management designs software architecture”, much closer to the negative interpretation; but that too can be interpreted in a more positive way as “… and we are not good at that, so let’s make sure to bring in the people who are good at it at important points”.
Self-Hosting GitHub is available under the name “GitHub Enterprise”, but there is nothing stopping a smaller company from getting an “Enterprise” license. At my job we are running self-hosted GitHub for less than 50 developers.