Nor can you know that it did. With the design and updates of the other Google apps (again, even before iOS 7 was revealed) it seems more likely that the YouTube design update was to bring it more in line with that than with anything specifically iOS 7 related.
I never said it did. Just that it seemed to be reflective of the flatter icon design that the iOS 7 UI has. It was someone else who seemed certain that it didn't, which no one has cited a source that indicates that.