He said "wow" - it's apparently a considered a foreign word, but it's the kind of foreign word everyone knows. I think teenagers occasionally say it when they're expressing ironic appreciation for something. ("Look at that guy's pink dye job! Wow.") The vowel sound in there is technically "correctly" pronounced as two syllables in Japanese, so the little boy stretched it so it sounded kind of "wah-oh."

(This has been your Trivial Linguistics lesson for the day!)