Actually, the syscall numbers are wrong! This reference seems better: http://blog.rchapman.org/posts/Linux_System_Call_Table_for_x...

Consider simple C program:

    #define _GNU_SOURCE
    #include <unistd.h>
    
    int main(){
        syscall(276);
    }

Strace'ing it shows the syscall used is tee, just as the reference I linked shows, and not pwritev as in OP's table.