Without more context it's really impossible to say whether that was a major I or not. It would be the only functional harmony in the entire pattern, so it seem

Without more context it's really impossible to say whether that was a major I or not. It would be the only functional harmony in the entire pattern, so it seems unlikely it was a I. A pentatonic melody by itself doesn't infer much in the way of harmonic progression. The only reason we hear C# as tonic is because he starts there and emphasizes it with repetition and mini-cadences that are primarily rhythmic in nature. There aren't any IV or V chords available with those pitches (or iii or vii for that matter, you can imply a ii but not very well). I would actually argue that interval actually is the most accurate term in this case. (Not that I didn't understand what was meant by the term "chord" though, and certainly wouldn't have been bothered by it)