The text you quoted is purely about copyright/licensing, not about the maintainers' sanity.

The more relevant quote is: "In order to keep SQLite completely free and unencumbered by copyright, the project does not accept patches from random people on the internet. There is a process to get a patch accepted, but that process is involved and for smaller changes is not normally worth the effort." Though this is still about copyright, not about being swamped with PRs.