To put it concretely, if the chance of a random gene mutation is 10^-4 to 10^-6 per gene per generation, and there are 37 trillion cells in a human body, each cell containing about 20k genes, (all numbers from quick google searches) then the odds of having NO genetic mutations occur in your body in one day would be (forgive my back of the envelope math, assuming a generation is 20 years): (1 - 10^-6)**(37 trillion * 20000 / 365 / 20). My calculator can't keep enough precision to make this nonzero. i.e., everyone has genetic mutations constantly which makes the title of the article completely uninformative.
Germinal cells reproduce very slowly, so the eggs and sperm have fewer mutations.
Also, cells inside the guts have some cascade method. The cells near the wall reproduce very seldom, but the intermediate cells reproduce faster, and the inner cells reproduce even faster. The inner cells that are reproducing fast die or get washed away, so the big number of possible mutations is removed. And the slow reproducing cells near the wall create more cells to replace the intermediate cells that replace the inner cells.