On the wiki page of this tag is written: This should only be tagged if the user interface (UI), logo, or related assets are visible.
But well... apparently, no one reads the wiki. The false tagging rate is literally over 99.9%.
Should we invalidate the tag? Or change the wiki? But then it wouldn't fit to the TWYS rule. And changing it to a meta tag doesn't seem right. ^{(I am not 100% sure yet what makes a tag a meta tag. If there is a wiki for it, please provide it to me. I can't find anything, and I'd like to know more about it)}
But keeping the tag like this, is nonsense in my opinion. It's as if other artists tag their pictures with clip_studio_paint , photoshop, or ms_paint ^{(I just found out some artists do this)} I mean, ms_paint could be a meme tag, for pictures without antialiasing. But the others? I would assume most people don't care about the software that's used to create art.

Source Filmmaker has the same issue. These tags aren't meant for what the image was created with, but whether something directly related to the software is visible (its UI, mascots, whatever).

watsit said:
Source Filmmaker has the same issue. These tags aren't meant for what the image was created with, but whether something directly related to the software is visible (its UI, mascots, whatever).

I can easily see people blacklisting the sfm tag because it tends to correlate with awkward low-quality animations. So it may have more utility to users in its current form than the technical correct use.
Thus in response to OP's post, the blender tag probably serves more purpose to differentiate itself from sfm than it would for the original intended purpose. Tagging the blender logo or UI is such a rare use case that it'll almost never be helpful in typical searching.

For a more statistical argument, 3d_(artwork) animated has over 400 pages of results as of writing
3d_(artwork) animated sfm gives 166 and 3d_(artwork) animated blender_(software) only 23. That sure as hell sounds useful for narrowing down a search if someone happens to remember what environment the animation was made in, but couldn't remember artist/character names. (And technically TWYS can still apply to sfm, its outdated shaders and limited texture mapping options make it visually different from other engines, pretty hard to say that about photoshop vs. gimp vs. krita)

ijerk said:
...for narrowing down a search if someone happens to remember what environment the animation was made in...

This could maybe work for sfm but not for blender. If you know a little more than "Object -> quick effect -> explode", you have no chance to differentiate blender from maya, 3d max, cinema 4d, etc