At JNB as you get airborne, in the dark, the end of the runway is already behind you. Typically V2 is 180kts. Ground speed is well over 200mph. With the nose rotating to 13 - 15 degrees, all you can see out the window is inky blackness. So it is very quickly onto instruments.
Simply put, you are out over the bush at about 100' doing 195kts, climbing. It is an interesting debate about the gear. The 744 had not stalled. It had a stick shake. So was close to a stall. With the gear now moving up you get a drag increase from the doors. No lift reduction. The gear does not affect the lift the wings are making. With the engines being fire walled, the drag increase is more than accounted for. The assumption in that statement is that they would have been using reduced thrust. It would be very unusual if they were using full power at JNB.
Wheels up or wheels down sinking into the veldt at 240mph is catastrophic. So the only reason not to raise the gear is the one of the doors, and the resulting drag increase. We could sit and debate endlessly whether the wheels should or should not have been left down, but what we do know is that the gear came up, and they flew it away to a safe outcome. So on some level, if not on all levels, the crew made the correct call.