It seems he already had an idea that his wife was just an ordinary lady who asked for some magical creature’s (namely me) assistance with the straw-into-gold incident. What he wanted to know was what did she give to pay the creature with. When he realized what it was, for days on end he was already searching for me even before I met up with the girl again.
When I did meet her and gave her the challenge, he never told his wife that he knew but took it upon himself to grasp the nettle: he searched the forests, he talked to a lot of beings, humans and non-humans alike till someone tipped him off that I was living in a certain part of the forest.