To assess the directoriness of an entry, include the path of that entry.

pkg_resources/__init__.py

@@ -2072,7 +2072,10 @@ def dist_factory(path_item, entry, only):
     """Return a dist_factory for the given entry."""
     lower = entry.lower()
     is_egg_info = lower.endswith('.egg-info')
-    is_dist_info = lower.endswith('.dist-info') and not os.path.isfile(entry)
+    is_dist_info = (
+        lower.endswith('.dist-info') and
+        os.path.isdir(os.path.join(path_item, entry))
+    )
     is_meta = is_egg_info or is_dist_info
     return (
         distributions_from_metadata

pkg_resources/tests/test_pkg_resources.py

@@ -335,7 +335,7 @@ def test_dist_info_is_not_dir(tmp_path, only):
     """Test path containing a file with dist-info extension."""
     dist_info = tmp_path / 'foobar.dist-info'
     dist_info.touch()
-    assert not pkg_resources.dist_factory(None, str(dist_info), only)
+    assert not pkg_resources.dist_factory(str(tmp_path), str(dist_info), only)
 
 
 class TestDeepVersionLookupDistutils: