He is referring to the dynamic range of the CD. As I understand it the dynamic range is the range of audible sound or tone from quietest to loudest. (Probably all the wrong terms but you can get what I'm saying).
The CD you referenced has very poor dynamic range. This is a product, again as I understand it, of pushing up the loudness of the CD which compresses the dynamic range.
This isn't a knock against Taylor Swift or that CD per se because the problem is almost universal these days. It is very hard to find a new CD or downloadable file that doesn't suffer from this production technique.
Search Wikipedia: "loudness wars" if you want to learn a little more.
What I hear in these compressed CDs, compared to older ones, is that first it is loud. Too loud for the corresponding volume setting on your gear. After that to me they sound too bright, too strident and they make my ears tired. They lack 'richness' in my opinion. Some of my favorite new bands have albums with nearly identical DR to the Swift CD you mention. Their DR hovers around 5 or 6. Well recorded CDs like Mark Knopfler's 'Tracker" and Steely Dan's 'Two Against Nature' have DR values in the 12-16 range. And they are fairly recent. They just made the effort.
I'm sure I haven't laid this out exactly or with the most precise terms but the effect is fairly obvious to me sonically.
New vinyl seems to fair better....but still not as good as good old vinyl.
Also, the DR can vary A LOT between different CDs of the same album when it comes to older CDs and "remastered" CDs notoriously have worse DR than the original releases.
