Maybe he means that he doesn't have to deal with bugs in a custom binary serializer.

It can only become corrupted by external factors; a lot of games I've worked on, in-game bugs could lead to corrupted saves being written out to disk. Since in this case we are just serializing lua data, unless the serializer itself has a bug, it will always write out correctly, and any issues become issues of game logic rather than anything else.

I don't think it does. I think he meant that if a save became corrupted it wouldn't do so silently, it would violently crash the game because of a syntax error.

It doesn't. But it makes them much easier to fix.

Edit: Igglyboo has a point too.