First of all, this can not be translated into hits directly. The data usage will vary, depending on content. Photos and videos can consume megabytes per visitor, whilst text consumes very little bandwidth.
For the number of visitors, you should look at your logfiles, typically /var/log/apache2/access.log – or install a tracker like Google Analytics, which will give you improved stats.
The reason it says eth0 since 12/24/2017 is that this is the use since that date (tracking started then probably). It seems that on the 25. and 26. there was no traffic, and thus not reported.
Furthermore, 2kiB means that you probably had zero visitors. At the most one, if it’s a really simple site.
You have a service called logrotate that rotates logs on a daily basis. The old ones gets moved, as you see, to a new filename, and optionally compressed, being given the .gz suffix.
Each line in the access.log generally means one hit, yes.