To most of the people watching the performance, the constant change in tempo and melody sounded fun and amazing. But to the musicians listening, they immediately recognized the high level of difficulty Enrique Valdez was injecting to the music.
Iris was bearing the most brunt of her music mentor constantly changing things up in her song. Eros and the other band members' skills might have improved a lot since their music collaboration, but they were still lacking in experience when it came to keeping up with the advanced and complicated techniques of a master musician like Enrique Valdez. As a result, she had to covertly wrest control of the music from her mentor again and again while making it appear as if Eros was still the one leading everything as the lead guitarist.
Her deception worked on most of the people, but the expert musicians among the audience and viewers noticed what was really happening.