Whilst reading To Kill A Mockingbird I came upon this sentence (full extract below):

It is better to say, built in spite of them.

To me, this sentence seems poorly structured, possibly even incorrect grammatically. I wouldn't have thought that a comma should be used where it is. I would've thought it'd be more appropriate to use a colon and perhaps even quotes around the correction.

I consulted someone I knew who said that they thought the sentence was perfectly fine as it was.

I have thought that it might have been written in this way so as to give the impression of Scout herself saying it but I am unsure.

Any opinions on the validity of this sentence will be very helpful, thanks!

The same sentence, as it appears in its original context, is as follows:

The Maycomb County courthouse was faintly reminiscent of Arlington in one respect: the concrete pillars supporting its south roof were too heavy for their light burden. The pillars were all that remained standing when the original courthouse burned in 1856. Another courthouse was built around them. It is better to say, built in spite of them. But for the south porch, the Maycomb County courthouse was early Victorian, presenting an unoffensive vista when seen from the north. From the other side, however, Greek revival columns clashed with a big nineteenth-century clock tower housing a rusty unreliable instrument, a view indicating a people determined to preserve every physical scrap of the past.