@carorees, You are absolutely right. The evidence is very strong that overdoing antioxidants is quite unhealthy. There are quite a few large, well-respected epidemiological studies (not related to each other) that have found that taking antioxidants increases the risk of death over a long period of time.
The explanation has to do with the fact that oxidation is used as a signal in mitochondrial processing. If you turn it off, the signalling doesn't work properly. One thing that doesn't happen is that cells that should self-destruct, because something is wrong with them, don't. (Apoptosis.) This can allow cancerous cells to survive.
In addition when you work against oxidation you work against the very "fat burning" that you are attempting to achieve with exercise. So taking too much antioxidant works against the benefits of exercise.
If you are interested in Mitochondria you can learn all about them in Nick Lane's wonderful book, Power, Sex, Suicide: Mitochondria and the Meaning of Life, which you can find on Amazon. His other book, Oxygen, the Molecule that Made the World also gives more insight into what "oxidation" and "antioxidants" really are about.
But getting back to the magic plums. This report is almost certainly based on research funded by the interests that market the plums. It won't hold up to any kind of unbiased scrutiny, and eating sugary fruit in higher than normal quantities is not going to improve anyone's health or help them lose weight.
The public's hunger for "superfoods" is insatiable because everyone would rather believe they can live forever eating something disgusting like kale, chia seeds or quinoa to which magical properties have been ascribed than do the hard work of NOT eating that it takes to actually lose weight.
Fortunately, this forum is filled with people who have figured out what it takes to lose and are doing a fine job of it.