Hello,
From my side, the question remains whether the contractor responded based on facts, or whether he interpreted the expert report in a way that might be more advantageous for him. I just couldn’t assess that at all…
In the first step, you should realize that the vast majority of BU/GU/GÜ/BT aim to realize a construction process as smooth as possible and want to generate references. There can hardly be no mistakes, as too many people work on the construction. A certain skepticism is always good, but I wonder where this preemptive negative attitude towards your contractor comes from? What would he gain from charging you—allegedly—too much for services? It’s not as if “left - right” pocket applies...
In the next step, I would suggest commissioning the geologist with the earthworks... if the ground continues to be as easy to handle, all the better for you. But I fear he will not want/cannot comply with your request ;) The contradictory statements can, by the way, also be due to the fact that at the time of the soil investigation no designs of the single-family house were yet available. I am on your contractor’s side and read the geological expert report similarly; you will have to expect considerable additional foundation costs.
Get another offer from a provider; possibly directly from a trusted civil engineer for the earthworks and from another general contractor for the basement execution. External, expert supervision would be even better; then you would have a permanent contact for doubts/questions of any kind ;)
We are building in the Steinfurt district in Münsterland.
Then you are still comparatively lucky, as construction prices there (still) remain somewhat reasonable ;)
Rhenish regards