{Adopted Kamado siblings Au explanation} Tanjiro and Nezuko were adopted by Giyuu. Giyuu is currently working to adopt Inosuke and Zenitsu next. Since he has adopted them, he's become more protective and worried about them being injured.
{Slight video explanation} Muzan injured Nezuko, and Giyuu was informed. Since Giyuu had adopted her and Tanjiro he was furious. So essentially he snaps at Muzan for hurting Nezuko,
