The thing is - and here I guess I have the same problem as phonefrog - if you look at the actual commit behind this “Bump security patch level to 2018-01-05” (https://github.com/LineageOS/android_build/commit/f05791524f2a57ae7473d1482a4e5fe9663cae58) it really only replaces that string.
And also all other entries in the changelog don’t look like they are related to security fixes.
For some outsider it might look like they just changed the label but not the content.