The ODP list sites with significant unique content. That doesn't say "sites without any non-unique content". Obviously, some sites contain both.
Also obviously, affiliate advertising (or pretty much any other kind of non-self advertising) is, by definition, not unique.
So the reviewer should ignore the non-unique content (if it's unobtrusive enough to ignore, and if it's distinguishable from the unique content) and review the site based on the unique content (if THAT is prominent enough to find easily, and can be distinguished from the non-unique content easily enough.)
How does that work in practice? Joe's Shopping site has three unique items handmade by his cousin. If that's all that's on the site -- it's listable, an easy call. But suppose Joe adds 20,000 items from dropshipper Vstore (or SMC, or whatever the upwardly-mobile pond scum are calling themselves these days). Now how do you expect the editor to FIND the unique content? He'd look at a few items, say "this is all Vspam affiliate"--and reject.
Or, suppose Joe sets up a blog blathering about "home improvement ideas" -- might be listable, depending on whether Joe knows what he's talking about. But ... if that blog appears to be "made for advertising" (that is, the advertising is so prominent, it seems advertising is the sole purpose for HAVING the blog) ... NOW the site exists "primarily for driving traffic to some other site", and in a very broad sense, that's what "affiliation" is.
Now, there's obviously a judgment call. But it's usually not that hard to make. A site is primarily to express its owner's ideas, or advertise its owner's goods and services -- or it's made primarily for third-party advertising. The owner knows which is which. Most other people can catch on, pretty quickly.