Sorry but that's not right, and I have had some experience of corporate governance. The whole point of non-executive directors is that they are independent from the company management on a day to day basis, and can therefore bring some sort of objectivity to board decisions. A non-executive chairman will act as a figure head for the company publicly and will if necessary act as a check on the executives if they are deemed to be leading the company in the wrong direction or failing to comply with its Articles of Association. In general, people holding non-executive directorships have other jobs, and perhaps other directorships. The time devoted to such a directorship is measured in days per year , not weeks, and certainly not months.
That is what "non-executive director of the board" means in the normal sense.
However, Lauda's job at AMG Mercedes F1 was described by AMuS as I posted above and widely published in German media - I think Merc wants to communicate to the public here that they are having an eye on the Brackley team and that Lauda will act in their interests, as he did already when he reached the Concorde Agreement for Merc.
Possibly the "non-executive director" was the title they chose, as for the real job description there is no fitting corporate title. What title does Dr. Helmut Marko have at RBR?