The article was very specific about that:
the company said that the total distance covered by its 96,000 trucks was reduced by 747,000km, and 190,000 litres of fuel had been saved
Though it basically contradicts that with:
it created an algorithm that eliminated left turns from drivers’ routes even if meant a longer journey
Interestingly, the quoted a Mythbusters experiment which confirmed the latter:
TV show Mythbusters tested the UPS theory by eliminating as many left turns from their route as possible. They found that an 8.3km journey became 30 percent longer (10.9km), but still consumed roughly 40 percent less fuel.
So, 2 conclusions:
1) you clearly did not RTFA.
2) the empyrical answer is "longer distance, less fuel".
And the OP's question remains - the why does the article claim distance was reduced as well?