not "when the author wrote this, he was trying to say"
And the first interpretation is relevant but wrong, whereas the second interpretation is true but irrelevant.
P.S. It seems that the author meant to say “it is not in general possible to find a given bug by examining the code”, i.e., "not (for all bugs B it is possible to find B)", which again is true but not relevant.
If a mathematician using the mathematical sense of the word general says "it is not in general possible to tell if a program will halt by inspecting it", they're talking about the halting problem, even if you've looked at lots of programs where you can tell if they'll halt or not, and your experience might be correctly described using the normal usage of the word with "in general I can tell if a program will halt or not".
I won't respond further.
I would add that (related to your "maintainability" point) ensuring the code is as simple as possible, and thus much more likely to be "debuggable by review", is a goal of review. Even that won't prevent bugs in the absolute sense, as you rightly say, but it boosts your probabilities.