That passage says they knew the way, it never said they recieved the way,
in fact, the passage itself proves these people were never saved, They just had knowledge. It says a DOG returns to his vomit. The dog was never made a new creature (new birth) it was still a dog. It had knowledge how to be saved, but it remained a dog, It was never saved.
Again, Why do you not believe in eternal security? Either you believe in God or you do not.