Considering the four noble truths, why do you think hesse states here that in the buddha's demeanor "there was no searching, no desire . ."?

Because to the non-noble eye Buddha's behavior at first instance could have seemed empty, and might have given the impression that he had no desire however as the Four Noble Truths explain and stand for, this is simply a projection of this specific mindset (buddhist) in which the individual is not longer seeking for personal satisfaction or material posessions (desire) but instead is completely focused of trascending into a spiritual plane.