This is not great reporting by the BBC. Most grievously, as others have mentioned, they don't mention the dosages this guy was taking.
The important point to grasp behind all this concern over "supplements" is that there's no such thing as a supplement. Everything that's not a food is a drug. If something is not part of a human diet somewhere - i.e. if it's been extracted and refined significantly - then it's a drug. (Does that mean you regulate supplements? No, because then you end up in ridiculous situations like banning high doses of water-soluble B vitamins. Banning certain brands and formulations is sometimes appropriate.)
Drugs have a dose-response curve, a median lethal dose, and all the rest. People taking "supplements" (taking them seriously, beyond taking a common-or-garden multivitamin you can pick up anywhere) should be aware of this and understand the risks.
"Natural" doesn't mean safe. Polio is natural.
Not all sets of genetics tolerate all "supplements" at recommended dosages.
In vitro is not in vivo.
Animal studies are not human studies.
I got into nutrition and supplementation through bodybuilding, and within that community the knowledge that things you put in your body can hurt you, do your homework is fairly widespread and well passed-on. Unfortunately that perspective hasn't really permeated broader fitness culture.
I think the attitude of "have this problem, take this pill" (without regard for risks or better options) is mostly at fault here. I'd argue corporate pharmaceutical companies have some culpability here - "ask your doctor if X is right for you" - or don't, and just bloody do some cardio or something.
This article is only interesting if you still conflate "green tea" with "natural" and "natural" with "safe".