I haven’t really seen anyone else talking about it yet, but it was one of my favorite details in the episode:
The journals can be wrong.They were just written by some guy! Sure he’s an incredibly smart guy, and he’s easily the most knowledgeable (human) on the supernatural in Gravity Falls, but the journals aren’t the be-all end-all that Dipper has been viewing them as. Neither is Ford.
Ford even lends the journal to Mabel for her “quest”, but she only opens it once to get the location of the unicorn to appear. After that the journal doesn’t appear again, but Mabel spends over half the episode trying to get the hair the way the journal described. In the end she finds a solution of her own method, and unlike what the journal described, it actually worked.
It’s been established that Dipper relies heavily on the journals, and I’m worried that it’s going to bite him in the ass.