I can find no specifics about it, so I assume it means there were at least 51 Republicans in the chamber at the time of the vote and zero Democrats.
The Senate passed a Resolution "honoring" Charlie Kirk also by unanimous consent earlier in the week. The Senate Resolution didn't contain all the garbage about how wonderful Kirk was like the House Resolution did, so I don't doubt that Democrats would be OK with it since it was basically just a condemnation of political violence.
RESOLUTION
Condemning the assassination of Charlie Kirk and honoring his life and legacy.
Whereas Charlie Kirk was horrifically assassinated on September 10, 2025, at Utah Valley University while speaking to a large group of college students;
Whereas Charlie Kirk was a devoted husband, father, and Christian;
Whereas, in 2012, Charlie Kirk founded Turning Point USA, a conservative campus advocacy group that quickly became one of the fastest growing college campus chapter organizations in the country; and
Whereas Charlie Kirk frequently engaged college students of all political backgrounds in open debates and discussion, encouraging civil discourse on college campuses and among college students: Now, therefore, be it
Resolved, That the Senate
(1) condemns the assassination of Charlie Kirk in the strongest possible terms;
(2) extends its deepest condolences and sympathies to Charlie Kirks family, including his wife, Erika, and their two young children; and
(3) honors Charlie Kirks commitment to the constitutional principles of civil discussion and debate between all people of the United States, regardless of political affiliation.