I would say that if you needed to quote the definition verbatim, that sounds a bit insane. However, if what was meant was that you missed out on a few key adjectives to more precisely describe GAS, then that would make sense. I don't see the point in learning textbook definitions word-for-word accurately, it seems pointless compared to actually being able to apply the theory you've learned.
As others have said though, VCE Sciences are indeed notorious for wanting some of the most specific and precise answers imaginable, and a good way to think about how to answer those kinds of questions is to say to yourself "What if I was to explain this to someone who has no idea what this thing is?" By framing the question that way, you will be cognizant about creating an explanation that's as holistic and specific as possible so that the layman has all the information they need to perfectly understand the concept(s).