All the references I'm familiar with say that letharia vulpina (wolf lichen) is poisonous. Which is what I have always heard. In this part of the world it has been used as a yellow dye.
One book says that in N. Europe it was mixed with wolf bait.
I don't know the answer to your question. Maybe it was your lucky day. Maybe your dosage was too small. Maybe you were mistaken on your identification of it and it was really usnea. Were you trying to make yourself sick?