That is correct.  In the Library List the Search function only looks at Online Libraries.  This is because the Online Libraries are complete and always up to date.

If Stardraw searched the Offline Libraries, even if the symbol you're looking for exists you might not have downloaded the manufacturer library that contains it, or you might not have synchronized your Offline Libraries since the symbol was published.

By looking in Online Libraries you get the very best chance of finding what you're looking for.