The GP poster's point was that the hosting service needs to prove to the consumers of the app that what's running on the hosting service is the same code they can browse through on GitHub.
When you're both the developer and the consumer, you can certainly prove this to yourself (to five nines of confidence or so) by just setting up the hosting yourself. But we're talking about the case of a centralized backend for a multiuser service, e.g. a forum, where the users want to not have to trust the moral fibre of the person who set up the server, but merely trust that the infrastructure used in the hosting guarantees that it can't run anything other than the codebase (that they control.)
When you're both the developer and the consumer, you can certainly prove this to yourself (to five nines of confidence or so) by just setting up the hosting yourself. But we're talking about the case of a centralized backend for a multiuser service, e.g. a forum, where the users want to not have to trust the moral fibre of the person who set up the server, but merely trust that the infrastructure used in the hosting guarantees that it can't run anything other than the codebase (that they control.)