"The room understands" is a common counterargument, and it was addressed by Searle by proposing that a person memorize the contents of the book.
And the room passes the Turing test, that does not mean that "it passes all the tests we can throw at it". Here is one test that it would fail: it contains various components that respond to the word "red", but it does not contain any components that exclusively respond to any use of the word "red". This level of abstraction is part of what we mean by understanding. Internal representation matters.