I agree that the take-off weight is not the issue. After all, Lamu, Kenya, is at sea level.
Here is a more detailed description of the rescue, and a longer video. The R44 is clearly flying, albeit right skid down (see video @ 2min 50 sec).
It just goes to show how flexible the R44 is, both from a longitudinal and lateral CoG point of view! You hardly ever have to worry about anything during normal ops.
Maybe this one is not quite normal though. Lateral envelope is +/- 3 inches. Using the assumptions for fuel, pax and cargo weight (50 kg for the hippo baby) from John R81, the lateral CoG comes out exactly at 3.0 in. Any bigger, like 100 kg as estimated by Thracian, and the lat CoG would be way out (4.6 in). Putting the rear pax on the left side could have helped, but who knows maybe their ops procedures require the loadmaster to keep an eye on the external load
P.S.: Calculations done using Co-Pilot for iOS