I read a sentence as below
Now, these results are not quite as bad as they sound. Although such adversarial examples are common, they're also unlikely in practice. Nonetheless, it is distressing that we understand the theory so poorly that this kind of result should be a recent discovery. Of course, a major benefit of the results is that they have stimulated much followup work.
This paragraph comments on an experiment of the theory. This theory works very well for most (i.e., more than 98%) examples, but fails on some so-called adversarial examples. People don't understand why the theory fails on them, because people thought they are easy examples.
I have a shallow feeling about the meaning of the sentence:
We understand the theory very poorly. This fact is distressing.
First, I don't understand why this kind of result should be a recent discovery can emphasize we understand the theory poorly. Then, I'm not clear why should be is used here. What is the difference between should be and is in this context ?