8.1 is correct. They introduced new functionality (minor version number) to the inspector. In general Node is very very good at following semver. Even for something as seemingly small as this, it requires the minor number to increment. If you follow along their issues on Github, they always tag PR's as needing a major/minor/patch increment. That way when merged it's really easy to see how the version numbers need to increase, or if they need to wait to merge something.

Technically correct, but Node tends to err on the safe side, specially when dependencies are bumped, as is the case. In this release both libuv and npm were updated.

The minor improvements are the new backwards-compatible functionality, such as identifying Promise triggers or making fs.Stats times available as numbers. Otherwise yes, you'd be right.

Node version numbers are weird. I'm not a node user but if this is semver sth. is certainly wrong, I see a major version update every other month here.