Al-Shamrani is an Arabic surname that is given to those who are a part of the Arabic tribe known as “Shamran” that exists in the southern part of modern-day Saudi Arabia.
Not much in Arabic yet, but there is a picture of him (taken from NBC) in this site from the area https://www.almashhad-alyemeni.com/151724
This might be his twitter account https://web.archive.org/web/20191206211844/https:/twitter.com/M7MD_SHAMRANI/status/1202930479089037312 and if that is the case he is an islamist.