The comparison with mathematics also makes sense here. It’s much easier to spot typos in other peoples’ work than your own for exactly that reason: when you read back what you wrote, you read back what you meant to write rather than what’s actually there.
Open any textbook (even a fourth edition of a famous one, written by an expert) and you’ll find countless typos. In fact, in a certain sense, the more expert you are the less suitable you are as a proof reader for such books.
One of my undergrad tutors taught complex analysis with a book she had written, and she offered a reward for any one who found an error. She said the best students never claimed the reward, only the people that had to study each word carefully.
You touched on it but I've experienced the same reading code when I knew what was intended by the code, regardless of who wrote it. I miss obvious but simple bugs because I only read what it is mean to do.
Open any textbook (even a fourth edition of a famous one, written by an expert) and you’ll find countless typos. In fact, in a certain sense, the more expert you are the less suitable you are as a proof reader for such books.