Weirdness in the daf

There is weirdness, in the Shakespearean sense, Shabbos at the end of daf 81b-82a, the daf shiur yesterday.  It is one of the stories brought on the infamous Chulin 105 group of agadatas.  According to the story, here in more detail, two Rabanim are in a boat and a witch stops the boat using a spell.  The Rabanim free the boat using the counter-spell. The witch laments that she is powerless since these are Rabanim are scrupulous in three matters that protect them.  They do not wipe themselves with clay vessels (ouch), they do not kill lice in the garments while wearing them, and they do not eat vegetables that are bundled.

Again I ask the same questions.  Are they protected by the practices or the counter-spell?  Do you need both?  How would following these practices help us if we do not know the spell?  If Rabanim were not allowed to learn goyishe things, how did they learn the spell?  What does this teach us about reward and punishment. that as long as you have your magic spells and practices, you are protected and do not need zchus of mitzvos?  There is probably a political parable in this story but I cannot speculate what it might be.