Not P but question about the word "synecdoche"

[Mike Jing]

>From DFW's The View from Mrs. Thompson's

LOCATION: BLOOMINGTON, ILLINOIS
DATES: 11–13 SEPTEMBER 2001
SUBJECT: OBVIOUS

SYNECDOCHE  In true Midwest fashion, people in Bloomington aren’t
unfriendly but do tend to be reserved. A stranger will smile warmly at you,
but there normally won’t be any of that strangerly chitchat in waiting
areas or checkout lines.

What does DFW mean by "SYNECDOCHE" here? I looked it up of course, but I
could not make sense of it in this context.  Here it serves as some sort of
a heading, and the other headings are: WEDNESDAY, AERIAL & GROUND VIEWS,
and TUESDAY.