Okay, let me try:
In Cape Town, there is CINX, the Cape Town Internet Exchange. At this exchange, CT MWeb and CT WebAfrica are peering. Therefore CT Mweb Clients can see WebAfrica servers as local. CT WebAfrica clients can see Mweb as local.
In Johannesburg, there is JINX, the Johannesburg Internet Exchange. MWeb is resident at this exchange, but WebAfrica is not. Therefore JHB Mweb Clients cannot see WebAfrica servers as local and transits the traffic internationally. JHB WebAfrica clients cannot see MWeb servers locally, and transits the traffic internationally.
In order that all Mweb and WebAfrica traffic is seen as local across the two networks, it requires WebAfrica to peer with Mweb at JINX. This is something that will happen "pretty soon" according to WebAfrica. Until then any traffic between the two networks that originates in, or transits via JHB will be routed internationally, and therefore subject to international latency.