To be sidetracked means to be distracted from your immediate plan, or from an important issue.
A track is a path, trail, or simple road for someone/something to travel on.
e.g. 1, I started to write my essay, and I needed to do some research on the internet. I got completely sidetracked and spent an hour on Facebook!
In the Blog 7 example the writer is telling a story about an ice fishing trip, but gets sidetracked and starts talking about rednecks.
See the STORY example: I got a little sidetracked there. Where was I?