To clarify, the test demonstrated that as you deflate the tyre, the footprint becomes longer, not wider as some people seem to think. The test was about footprint shape, not sand performance.
On the other hand, there was another article done by Roothy on Milo when he changed from skinnies to fats, and he preferred the fats.
The other misconception is that a tall skinny tyre will provide more floatation than a wide tyre which is also incorrect. a 7.50R16 (31") skinny will lengthen when deflated to the same length foot print as a 31x10.5 for example with pressure adjusted to suit the carcass. The fat however has greater width so the larger footprint provides greater floatation.
With regards to mud traction, a skinny will sink quickly, but a fat mud tyre will also clear the mud if it is spun and it will bite down. You will notice that all comp mud tyres, all comp sand tyres etc are very wide tyres - there are very few skinnies out there. Comp tyres are designed with a purpose in mind and to do that well - so they are wide. Likewise many people say that sand tyres should be closed pattern highway tyres, but all comp sand tyres are open pattern and paddle design.

