The paper you cite and every single paper on artificial neural nets learning to "do maths" or "do arithmetic" etc that has every been published. are only showing neural nets learning [1] the results of specific operations between numbers up to a certain value. There is no work that shows neural nets learning to do arbitrary arithmetic operations on arbitrary numbers.
To put it very clearly: neural nets can't learn to "do maths" in any general sense.
Neural nets are infamously incapable of generalising beyond their training dataset and the OP is very reasonably skeptical of comparisons between artificial and natural neural networks, given that only the latter are known to be able to generalise from few examples seen very few times.
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[1] As in overfitting to.