Can't a noun in plural form be described with a noun in singular form? of course it can. here is an example:

> These workers make a lot of mistakes when they work since they are
> new to this job. **they are not the main reason we are losing money**, the state of the market is.

And even a simpler example:

> These people are my family

And also

> We are a team!

the quote you provided is perfectly fine and makes the same sense:

> These (things you need to do) are not (the) homework (you are
> obligated to do)