Not only but usage

[markhedder]

"He chose an animal who he feels is the most powerful out of not only the tournament competitors, but any of the large number of dogs in the area over the past couple of years."

I think the sentence is saying that he chose someone that fits the criteria of A and B. So it has to be A and B, neither can be excluded.

But someone else is telling me that the sentence is saying for the animal he chose, the pool of possible answers does not have to be only in A, it can exclude A and only be in B. Vice-versa.

Who is right? If I am right, can you give a clear, compelling argument on how to explain my case because I tried explaining it in simple terms but he still doesn't agree. Maybe even a better way to write the sentence.
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[PeterL]

The 'not only... but' construction can be used in several ways. The usual way is for the B types to be somewhat different from the A types. The A's can be a restricted category that excludes B's, or it can include the B's. There could be just the A's, or not just the A's but also the B's.

I love the way that Beard and Kinney used that construction ironically in Bored of the Rings.