You miss the point - a virus with a 1% death rate of those infected, that mutates into a virus 50% more transmissible, with a 1% death rate of those infected, is obviously likely to kill more people.
The UK variant which will be the dominant strain in the USA in a couple months is more deadly, and I believe the same is true for the South Africa version. Both more infectious, and both more lethal.
That's not what is in the article. It says "“there is a realistic possibility that infection with” the country’s dominant Covid-19 variant “is associated with an increased risk of death compared to infection with” other strains of the coronavirus."
What they are saying is basically "we do not know".