For now, I'll give up.
I spent a few more hours today researching the two families, but largely unsuccessfully.
There actually was a Stieger family in Grabow, Mecklenburg. I found the name there in 1808. In the 1819 census they are called Siegert, with a note that they came from Ahrensfelde, Kingdom of Saxony. Because of the completely different dialect, it may well be that the name was misunderstood.
For the shepherd Schmidt from Bohnert in Schleswig-Holstein I have unfortunately no result at all. Although the church book Kosel has registers, the name was not to be found.
But since he was a shepherd, it may well be that the family lived there, but moved around. Therefore, the birth around 1832 may well be recorded in one of the neighboring communities. Rieseby I have also already looked up, there he was not born.