The prefetch pulls the file and validates the sha256 and then names the file to 80fb54a6645727d3d26c7913113df57688f9f955 .
The extract is just extracting the file with the name 80fb54a6645727d3d26c7913113df57688f9f955.
We are not doing any calculations or validations with that file name, which happens to be the sha1 of the file as well. if you changed that name to something else, like bob, the action script would still work the same.
prefetch bob sha1:80fb54a6645727d3d26c7913113df57688f9f955 size:5057 http://site:52311/Uploads/80fb54a6645727d3d26c7913113df57688f9f955/testing.txt.tmp sha256:bccbc9d3ec7ddb5393109a5a6a055b3b49ba54cd175f14731938b8cc9f671fd3
Use of sha1 in the file name is cosmetic in that part of the action script.