To be honest with you, I usually find cheaper fares (o/w or r/t) from Africa to Europe than the opposite and it's even more accurate in premium classes!
Then, the main reason why many of us read this section is to fly upfront at the lowest possible price in a way to earn tons of miles. In this specific case of TAAG, it looks like many members were discovering its FFP Umbi Umbi and how it works thus proving not being the priority.
Of course, only a handful of travellers are interested to fly from JNB/CPT to LIS/OPO, but considering many threads here showing how people would go out their way to visit Siberia, Viet Nam or Florence - it is safe to say that Portugal or SA could be included in a larger trip and not for the sole purpose of it - unless one likes flying obscure/exotic airlines.
Finally, I can not afford first class trip in cash at the usual fare bracket (unlike spending FB miles), thus this deal looks attractive enough to share for those willing to experience relative luxury with a dash of adventure without the usual cost attached (such as LH, AF, EK and the likes although with a alleged better service).

Anyway, thank you for sharing your first hand experience and the tips about LAD