I think the point is that "Non-existent words should be easy to check for" is a useless metric, because plenty of answers are non-existent words. Proper names and things like that, many of which the computer may not have in its database.
So it can't simply blindly reject answers that are non-existent words.
An example of how this computer could make a mistake: Sometimes two proper names are crossing at a vowel. If you don't know either name, you sometimes have to guess blindly at the answer. (This exact scenario is rare in crosswords like the Times, but do occasionally come up, and similar scenarios exist.)
Comments
I think the point is that "Non-existent words should be easy to check for" is a useless metric, because plenty of answers are non-existent words. Proper names and things like that, many of which the computer may not have in its database.
So it can't simply blindly reject answers that are non-existent words.
An example of how this computer could make a mistake: Sometimes two proper names are crossing at a vowel. If you don't know either name, you sometimes have to guess blindly at the answer. (This exact scenario is rare in crosswords like the Times, but do occasionally come up, and similar scenarios exist.)