What does Carnegie mean when he writes that “The ‘good old times’ were not good old times” (Foner 33)?

It means that the old times weren't as good as the phrase 'the good old times' made it seem.

explanation:

What Andrew Carnegie meant by this is that although we may use the phrase

“The ‘good old times’, those times were not really good times. This is because things were not clearly as good as it is today compared to those times. Going back to those times or old conditions would be disastrous as the good old times were not quite as civilized as we have it today.

From the speech from which he said these words, he said neither master nor servant were as well situated as they are today. This means that life wasn't very easy or comfortable in the old times compared to today.