Hi, Yes I think it is strange too, that none of his relatives were interested in his Swedish background. It must have been such a difficult (and exciting) trip, to go all the way to America and start a new life, far far away from their loved ones...
Anyway, what I can do is check the Swedish churchbooks to find any carl jonsson, or similar, who was born around Stockholm, at that date. I dont know if you are familiar with the Swedish books, but the priests also wrote when people emigrated,
Because, i do not know if there is anywhere where they have to declare where in Sweden they were born.
I have trouble myself with a relative who emigrated. I know excactly when and where he was born and that he bought a ticket to New York. But after that I have lost him. But I have just started searching for him so I have many ways left :)