I've read through the discussion here, and I must say: It does not matter whether the statement in Swedish is true or false. It is what it is. The question is how best to translate it. In other words, it doesn't matter whether garlic is a white onion or not, just whether the Swedish sentence is saying that it is ...
The point of the exercise is to show the difference it makes in Swedish when you use a compound noun rather than a space. Hence:
- vitlök = garlic
- vit lök = white onion
If you switch the two around, you get a different sentence. And while the truth contents may be the same, it's not really a direct-enough translation in a language course.
In English (at least in my dialect), these are white onions and this is a yellow onion (or possibly a sweet onion; I can't tell them apart visually). These are both gula löker?
Edit: another comment, with a link to a Swedish supermarket's website, indicates that the Swedish word for white onion is "silverlök"