Congress declared Confederate soldiers to be American soldiers.
Congress said it would provide gravestones for Confederate veterans and pay pensions to their widows (in 1958, after virtually all Confederate veterans were dead), but it didn’t say that they were to be considered US veterans or soldiers.
Confederate Soldiers Are Considered U.S. Veterans Under Federal Law-Truth! https://www.truthorfiction.com/confederate-soldiers-are-considered-u-s-veterans-under-federal-law/
Confederate Soldiers American Veterans by Act of Congress https://www.veteranstoday.com/2013/04/03/confederate-soldiers-american-veterans-by-act-of-congress/ https://www.veteranstodayarchives.com/2011/04/14/confederate-soldiers-are-american-veterans-by-act-of-congress/