No need for a database or complex backends
Building and hosting are decoupled
I don't get it, since when building a static site requires a database? Are they referring to eliminating some kind of CMS?
So what we have done is we keep all data on their place ( depended github repos ), grab them before build time, and generate static content based on it. Moreover, we have some mechanism to target particular branches/commits on depended repos, and control when we want to trigger our pipelines.
So, replaying directly to your question - no, building a static site not require a database. JAMStack architecture is helping us to provide and manage our specific data sources.
This is pretty much in contrast to other stacks, where more often you will not need a database at compile time, but only at runtime. Of course, the statically generated HTML will not update unless rebuild and deployed (except if you use a hybrid static/dynamic approach using Javascript or the completely server-side rendered mode, both of which are also supported by nextjs).