Note, we are told that, "Anthony awoke to laughing and applauding," in other words, he woke up by an unusual action, "laughing and applauding". This causes Anthony to wonder confusingly what had occurred, which fits in with the definition of the word, "quizzical".
The word quizzical is an adjective that is often used to denote the expression of someone who appears to be confused or amused.
Personification. The author is treating the river like a person. When an object/animal/thing is talked about like a human being, then it is personification
