Anki has a long history of not-so-great version numbers. 
Semver is a bit of a tricky subject. From the perspective of add-ons, it’s a breaking API change, and you could argue that should make it 3.0. But that’s not really practical - because add-ons are so tightly coupled, we’d end up bumping the major version every few releases that way. So I mainly focus on what’s exposed to end users outside of add-ons. This update doesn’t change how cards are stored on disk, or require a downgrade before moving back to .48 for example.
When we upgraded to Qt5, that involved a bump to 2.1. But that was a much bigger move, as we had to transition from WebKit to WebEngine, and asynchronous JS requests, and it wasn’t feasible to support Qt4 and Qt5 in parallel. That is not the case this time - the web API is closer, and Anki still works on Qt5.
But regardless of whether it makes sense or not, it’s not a change that can be easily made at the moment, because AnkiWeb’s update and add-on handling code was hacked together while I was busy with the 2.1 work, and it wasn’t written with support for future minor versions in mind. Teaching it how to deal with semantic versions (or even just a single new minor version) will take some time, and it’s probably not something I’ll be able to get to before this release unfortunately.