I no what you mean EWO, but yes what the author is speaking about is mixing other breeds, he uses the word (breed) not bloodlines or strain, also on that same chapter he says and I quote,

"When a Napolitan Mastiff/Pit bull cross is matched with a pure pit, the cross bred dog can often bite down the pure pit down. Then he will (tend to) just stand over his "prey" uninterested in continuing. This is true. And it is behind the excessively hard biting (pure bred on paper) match dogs that when rolled to see what they have bite very hard, only to quit standing up when not even bit."

One more thing he says is of a friend of his who has bred his own type of catch dog a Pitbull/Grate Dane/Napolitan Mastiff blend, which he claims to be as game as a Pit bull but having more endurance and I quote,

"Then he bred pit for many generations, in and out of Fankie and Baron until he had catch fogs that look identical to pure pit, have the gameness of pure pit, but way beyond in endurance and power and effective focus. His dogs have a very tough coat and a harder bite than the average pit. They are specialists. Catch is their game and you can't find any better. Pit Bull purists scoff. Go ahead. For me this Riddle breeding is one super surreal dog and a sui generis among Bulldogs"

This is in the revised DVS book which contains a second book titled Epilogue, it's interesting that he says that this Neo/Pit crosses are not game but his friends dogs are as game as a pure Pit bull.

In all this is a good book, I just find this statements ti be strange.