I take your point - I had read into that quote the implication that there are other cases where something resembling carrying had been seen, but even just adding the properly-aligned digits modulo 10 would be impressive. I would, however, like to see more evidence that this seems to be happening more often than by chance, and is unlikely to be explicable in terms of the specific numbers in question appearing in close proximity in the training data, before I am willing to say that it is the most likely explanation.
Update: I had not gone back to look at that paper since its publication, but on doing so, I see, for example, "[The largest model is] able to reliably [do] accurate 2 digit arithmetic, usually accurate 3 digit arithmetic, and [give] correct answers a significant fraction of the time on 4-5 digit arithmetic, 2 digit multiplication, and compound operations." Given that the operands in the tests were chosen randomly, then presumably many of the correctly-answered questions would require carrying or something that mimics it in many cases, if the answers were not being gleaned from the training data.