Funny from a book

I was sitting reading science to my 2 youngers. They need to classify leaves. So the book is telling them all about collecting leaves and it's ok and all that and then we come to this sentence:

If you cannot find many leaves outside, go to the grocery store and buy a mixed salad package.

We all had to laugh. Now before anyone gets upset, I know that for some this would be a necessary thing. I can completely understand the need in the inner city for example. But here in the 'burbs where we do still have a decent number of trees, it hit all of us as funny!