As abergal wrote, not carrying the “1” can simply mean it does digit-wise addition (which seems trivial via memorization). But notice that just before that quote they also write:
To spot-check whether the model is simply memorizing specific arithmetic problems, we took the 3-digit arithmetic problems in our test set and searched for them in our training data in both the forms “<NUM1> + <NUM2> =” and “<NUM1> plus <NUM2>”. Out of 2,000 addition problems we found only 17 matches (0.8%) and out of 2,000 subtraction problems we found only 2 matches (0.1%), suggesting that only a trivial fraction of the correct answers could have been memorized.
That seems like evidence against memorization, but maybe their simple search failed to find most cases with some relevant training signal, eg: “In this diet you get 350 calories during breakfast: 200 calories from X and 150 calories from Y.”
As abergal wrote, not carrying the “1” can simply mean it does digit-wise addition (which seems trivial via memorization). But notice that just before that quote they also write:
That seems like evidence against memorization, but maybe their simple search failed to find most cases with some relevant training signal, eg: “In this diet you get 350 calories during breakfast: 200 calories from X and 150 calories from Y.”