Calestous Juma failed to interpret the tariff schedule correctly and missed a rather important point.
But, and it is a big but, he either failed to notice, or for some reason ignored the other row headings in the table. MFN, GSP, LDC.
MFN is Most Favoured Nation, meaning the rate under WTO MFN rules, applied to all countries where there's no WTO approved exemption.
Exemptions are by Free Trade Agreement or by WTO approved derogation. The latter are what GSP and LDC refer to.
This means that the row headed LDC should be used countries identified by the UN as least developed countries. So a ZERO tariff, not 7.5%MFN tariff should apply.
Under GSP+ countries encouraged to maintain sustainable development and good government are also rewarded with zero tariffs.
A consequence of tariff reduction/elimination is a commercial advantage over countries on the MFN tariff.
Are you surprised by this? Are you surprised that Brexiters don't seem to be aware of this?
Though I have to say, if you do so, you'll be the first Brexiter I've explained this to who does.