Even if they know the meaning of "shallow" (which is not a really common word AFAICT), they might not know what it means in this context.

Adding an entry to glossary might be a better solution.

In this context I think the best solution would be to actually show the implication of having a shallow copy with another short example (hijacking the reader to some other page where they can find some in-depth description of what "shallow" might do more harm than good).