While from the test's perspective they are both dynamic, it is attempting to reproduce the conditions of static content in the real app.  Here "static content" means a document that references an l10n ID that was used to generate the inlined JSON.  The term "dynamic content" means an l10n ID that is not present in the inlined JSON.

It seems some comments might help make it clearer.  @fabi1cazenave, how can I collaborate here to add comments?  Post another patch to the bug?  I've never used multi-author github pull requests.