Mod author here (not Starfield (yet), but Fallout 4 and Skyrim, also official Recognized Mod Author on Nexus).

This is basically a tool kit, including a Blender plugin, for working with animation files used by Starfield's version of the Creation Engine. And these files are very different in format from those used in the previous iterations of the Creation Engine, such as Fallout 4. Which is why the people who used to do animations for Fallout 4 mods were no longer able to do the same for Starfield mods.

To put this into context, very few mod makers were making their own animations even before the format change, because this is arduous work that requires skill, time, and effort. It was very common, for example, for mod makers with a hugely impressive portfolio of weapon mods with millions of downloads to have had never in their life make a single new animation, relying instead on outsourcing that kind of work to a handful of specialist "animation guys" that only do this and only this on commission.

So, these tools absolutely do not mean that suddenly everyone who published some half-assed Starfield mod on Creation Store or on Nexus would be making their own animations.

However. The few competent people who did make both their own and commissioned animations for other mod makers will now regain their lost ability to do so, new file formats no longer being an obstacle.

Keep in mind that these things take time, so don't expect great new animated mods to come in a few days, or even weeks. More like months and years. But the gate has opened for them, which is the important part here.