The thing about that example from Cambridge is that the words are complete - every letter is present in each word - just in the wrong order. So when we look at the shape of the word, we're looking at both the first and last letters, and also the length and shape of it.
What happens with a lot of spelling errors is that letters get left out, or the wrong letters are used altogether. I've seen some shockers in these forums! But sigh, I tolerate you all anyway...
