pull: granular pull of a single file triggers full imported dataset download

[shcheklein]

Bug Report

Description

Looks like dvc pull dataset/file triggers the full dataset download if dataset is an import from another repo.

Reproduce

mkdir test-granular-pull
cd test-granular-pull
git init
dvc init
git add .
git commit -a -m "init dvc"
dvc import https://github.com/iterative/dataset-registry fashion-mnist/raw
git add raw.dvc .gitignore
git commit -a -m "import raw data"
rm -rf raw/*
rm -rf .dvc/cache
cd raw
dvc pull t10k-images-idx3-ubyte.gz

Produces 1 file modified and 4 files fetched and downloads all files.

Expected

I would expect to see 1 file modified and 1 file(s) fetched

Environment information

DVC version: 2.3.0+ed2a0b
---------------------------------
Platform: Python 3.8.9 on macOS-10.15.6-x86_64-i386-64bit
Supports: All remotes
Cache types: reflink, hardlink, symlink
Cache directory: apfs on /dev/disk1s1
Caches: local
Remotes: local
Workspace directory: apfs on /dev/disk1s1
Repo: dvc, git

[pmrowla]

Resolved by #9246