It seemed like a gratuitious swipe to nail the orchestra members for being "glued to their sheet music", while Ms. Martinez played her concerto from memory. I would bet virtually every orchestra member can play more than one concerto for his/her instrument from memory and, given the invitation, would be happy to do so. And I'm pretty sure Ms. Martinez does not play symphony transcriptions from memory, either.
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And, why is it "sheet" music, anyway?