I was doing a Q&A in Software testing, and in one question they have :

Q) Which of the following is non-functional testing for an e-commerce website?

a) People can buy goods b) people can return faulty goods c) security of system during transaction d) 1000 people can log into system at same time.

ANSWER: d) 1000 people can log into system at same time.

And the explanation is:

comment: In non-functional testing, the quality characteristics of the component or system is tested. Non-functional refers to aspects of the software that may not be related to a specific function or user action. Eg. How many people can log in at once?

I 'am confused about the answer, because in my knowledge the security testing is part of the non-functional testing, so the answer will be also "security of system during transaction"

What do you think?

Thanks for your help,