McDonalds coke is awful. It is the worst possible product out there. But the article is right, McDonalds coke taste different, because it is. The secret ingredient is water (which explains the watered down taste.) A long time ago McDonald made an agreement with CocaCola to add slightly more water than anybody else. This allows them to sell more coke with the same amount of syrup.
One thing they do right, is cleaning the entire machine on a regular basis. It is amazing how much better the product tastes from a clean machine
I always found McDonalds coke taste sweeter than coke found elsewhere, especially compared to canned coke.
Higher syrup ratio or less water pressure results in more syrup, and therefore sweeter. McDonald's ostensibly aims for uniformity, but gross underpayment and poor treatment of workers leads to low goodwill and less caring for doing things "properly." Half the time, carrot slices or tomatoes are missing from side-salads and 40% of the time orders have mistakes.
I was told that a-b testing coke and Pepsi results in statistically insignificant margins.