How can a bloom-filter not be just a post-process effect?
As I said, it might not be effecting something as simple as a single post-process effect typical of a bloom filter - what I mean is, they suggest the effect can be applied as a post-process effect but with shader-specific results -
Post processing shaders can be created in the node based shader editor, just like any other shade
Any pass can be used as the input to another pass, allowing for elaborate effects
it suggests that more than a simple screen-wide post-process effect takes place - the specular channel of a certain material (defined in the shader) could be re-rendered as a post-process effect pass, creating a bloom effect only as a part of a certain material/shader, and not as an entire screen effect. Yes, it may require another render pass, but so what? It is described as an elaborate effect, thus probably requiring more rendertime.
This would explain how the elf's sword can have such an extreme glow, created as a shader but rendered as a material-specific post-process effect, but there is minimal glow around the background scenery.