A single “letter” of DNA was deleted, turning parts of the gene after the change into gibberish from the point of view of vitamin C production. There are thousands of ways that the gene could have been broken, thus, on the basis of the fact of evolution, it was predicted that the apes would share the same mutation. That prediction was successful.
There are many other examples of broken genes telling the same story. Unless God is trying to trick us, humans and other apes share a common ancestor. Kern also says that Grow “did not mention that guinea pigs also have the same deficiency.” Correct, but Kern has himself made an omission. Guinea pigs, unlike the apes, don’t have the same mutation that caused the deficiency in humans as you would expect if evolution were true. I suggest reading “The Making of the Fittest” by Sean B. Carroll for more on this subject.