It's actually a good analogy. It doesn't mention "timbre" and doesn't claim that timpre is not part of the compositional process. A classical composer can indeed specify timbre to a certain degree, and modern composers created new kinds of scores which offered more specification means for many features related to "timbre", but there is still a difference between composing music, playing music or building instruments in formal musical education.
It's actually a good analogy. It doesn't mention "timbre" and doesn't claim that timpre is not part of the compositional process. A classical composer can indeed specify timbre to a certain degree, and modern composers created new kinds of scores which offered more specification means for many features related to "timbre", but there is still a difference between composing music, playing music or building instruments in formal musical education.