First, I'm not a lawyer. That said, it doesn't need to be in the license agreement. You'll find the same to be true for Photoshop, Word and other programs. Things you create with Spine are your IP, you own them and you can do what you like, sell them, etc. Things you create with Spine include the Spine project file and things you export: JSON and binary data, images, texture atlases, and video.

Note that creating derivative works using the official Spine Runtimes (which load, render, etc the JSON and binary data you've exported from Spine) is granted by licensing Spine. So, while you own the JSON and binary data and can sell it, anyone who wants to use the official Spine Runtimes still needs a Spine license. Of course it's their data and they could write their own, clean room runtime implementation instead. Using images and video of course doesn't require a runtime.