Fix wording in pyproject-toml.rst license section

Author: brettcannon

source/specifications/pyproject-toml.rst

@@ -260,9 +260,10 @@ as specified in :doc:`/specifications/license-expression`.
 Tools SHOULD validate and perform case normalization of the expression.
 
 This key should **only** be specified if the license expression for any
-and all distribution files generated from the :file:`pyproject.toml` is the
-same as the one specified. If the license expression will differ then
-it should either be specified as dynamic or not set at all.
+and all distribution files created by a build backend using the
+:file:`pyproject.toml` is the same as the one specified. If the license
+expression will differ then it should either be specified as dynamic or
+not set at all.
 
 Legacy specification
 ''''''''''''''''''''