The enzymes practical was linked to enzymes topic though?
and standard deviation is just a topic that can come up related to any of the topics so its just something you need to know for any future exam.
I think it was nice of them to give you any guidance at all and i think by telling you about the exact practical and standard deviation topics they might as well just give you the exam questions haha... for future, just make sure you have a basic knowledge on everything and THEN focus on the given topics.
And at least you've been caught out now and not for your real exam!! It's all part of the learning curve