Add a comment on the potential implicit type up-casting (#63905)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63905
as title
ghstack-source-id: 136590703
Test Plan: N/A
Reviewed By: mrshenli
Differential Revision: D30527929
fbshipit-source-id: 69402bbfa87cfd8fc166ce313cde9736ee072589
