+0
The passage below comes from SAT Power Vocab as follows :

https://books.google.co.kr/books?id=7Xk0AQAAQBAJ&pg=PA122&dq=%22Using+only+the+entirely+unexcitin...

Using only the entirely unexciting groceries she found in the refrigerator, the master chef concocted a fabulous seven-course meal that left her guests shaking their heads.

In these two underlined parts, 'fabulous' seems to be used in ironical sense, I mean it actually doesn't used in positive sense the word literally has; rather it is used negatively because the meal made guests shaking their heads, that is, guests didn't like her food at all.

Am I right?

Regards.
+1
It's not a matter of "yes!"
It just means that they couldn't believe that the master chef managed to do that. They shook their heads because were amazed/astonished/astounded; not because they disapproved in some way.
Comments  
I don't think you're right. I think the author is praising the master chef for being able to cook a seven-course meal using ordinary ingredients.
.... shaking their heads in awe/amazement
Site Hint: Check out our list of pronunciation videos.
Thanks a lot for your immediate reply, teechrEmotion: smile

But Wikipedia seems to say otherwise.

https://en.wikipedia.org/wiki/Head_shake

A head shake is a gesture in which the head is turned left and right along the transverse plane repeatedly in quick succession. In many cultures , it is most commonly,[citation needed] but not universally, used to indicate disagreement , denial , or rejection .

Different cultures assign different meanings to the gesture. Shaking to indicate "no" is widespread, and appears in a large number of diverse cultural and linguistic groups . Areas in which head shaking generally takes this meaning include Indian subcontinent , Middle East , Africa , Southeast Asia , Europe , South America , North America and Australia .
However, in most Southeast Europe , e.g. Bulgaria , Greece and southern Albania , it is used for the opposite purpose, to indicate affirmation, meaning, in fact "yes". In these regions, nodding in fact means "no" as well, the complete reverse of most other places in the world.

If there is still something that I'm missing, can you suggest any example sentence which shows that 'shaking their heads' means a definite YES.

Thanks in advance.
 teechr's reply was promoted to an answer.
Right! Now I can grasp the full meaning of the sentence.
Thanks a lot as always, teechr.
Students: Are you brave enough to let our tutors analyse your pronunciation?