The source discusses why non-assertive expressions are not evaluated by the same correspondence between an asserted relation and external reality that characterizes reports.
“Close the door” asks for an action rather than informing us that something has occurred. “Is the door closed?” requests an answer. These utterances may succeed or fail in their respective purposes, but they are not primarily assertions to be judged true or false.
The key is the utterance's function, not merely whether a noun or a verb is present.