What differs a short story from a novel is definitely not “economy words and filler content”. The two are very different narratives, structure and concepts. You don’t usually start writing a novel and realize it’s a short story or vice versa. Even if you do, then you rethink your whole structure.
Economy with words and filler content might differentiate a good from a bad novel, but not a novel and short story.
I think of movies as the equivalent of short stories and serialized series as novels. That distinction also seems to hold when it comes to adaptations.
“Filler” is very subjective. A very long chapter going on a tangential introspective mourning thoughts may be viewed by some, as it “doesn’t move the plot forward”, but it can be the most pungent point of emotional connection in the entire novel for others.
Sometimes going on talking about minor characters routine is kind of the main point of an author’s intention, but it may read as “filler” by some.
Or something like Brandon Sanderson books, where his fans enjoy spending more time in that universe, but make their novels very long.
"A Canticle For Leibowitz"; "The Stranger"; "The Fall"; "Childhood's End"; "Riddley Walker"; "The Martian Chronicles"; "The Sea of Tranquillity"; "Animal Farm"; "Catch 22"; "The Catcher in the Rye"; "A Clockwork Orange"; "Dr. Strangelove"; "To Kill A Mockingbird"; "The Little Prince"; "The Unbearable Lightness of Being"; "Lord of the Flies"; "Charlotte's Web"; "A Tree Grows in Brooklyn"; "All Quiet on the Western Front"; "The World According to Garp"; "Invisible Man"; "Flowers for Algernon"; "Sophie's Choice"; "The Road"; "All the Light We Cannot See"; "The Goldfinch"; "Atonement"; "The Curious Incident of the Dog in the Night-Time"
Given how long he's been writing (he sold his first story in 1989), the fact that he's only published 18 short stories and no novels in his entire career probably says a lot about his approach.
Stephen King, to me, suffers from the exact opposite.
His short stories are amazing and right to the point, but most of his novels are filler and would probably work better as short stories. In novels King has to answer questions he can skip in short fiction which is why his novels always end so unsatisfactory ('it was aliens all along!').
I wonder if that in itself made his works higher quality: no pressure for high word count, and thus economy with words and no filler content.