Two separate paragraphs.
That’s how I read it too: as a confirmation of Escrodas’s statement, and with an empty line afterwards indicating that lay speculation can shed little light.
Now there are different statements, also here in the thread.
You just have to read the plan correctly, both image and text. You don’t need to mind the awkward wording; the council members probably wanted to achieve clarity. Many builders today build without a basement, simply with a "slab-on-grade." Its upper edge is that of the concrete slab—otherwise, with an unfinished floor, some laypeople might wonder whether it means the screed upper edge beneath the tile adhesive. That houses with basements should then be one floor lower is certainly not the intention of the development plan. You will also encounter other terminological confusions, e.g., "wall height" being used to translate the eaves height on flat roof constructions, and similar things.
"For the Müller family we approve
You don’t need to worry about that; there is the principle of discretion binding = the same decision with the same facts.
I summarize:
You may build the upper floor regardless of "with or without basement."
Because of the different reference heights for eaves and building height (for pitched roofs: practically "ridge height") it can be a bit tricky to calculate the knee wall height and roof pitch optimally.
Your municipality is not the first and not the last whose development plans have to be read three times.
In Ecroda’s posts you already find good guidance, with professional experience and clearly separated what is knowledge and what is speculation.