C++: mtime: ls and mtime don't match

Question

I'm encountering a situation where I think the mtime returned by ls on the command line differs from the mtime returned by calling stat in my C++ program. Does anyone know why this might be the case?

Because this is a university assignment, I can't share my exact code with you. However, this is essentially what I am doing in my program:

    DIR *dr;
    struct dirent *mydirent;
    dr = opendir(somepath);
    if (dr) {
        while((mydirent = readdir(dr)) != NULL){
            struct stat sb;
            stat(mydirent->d_name, &sb);
            fprintf(stdout, "%s %d\n", mydirent->d_name, (int)sb.st_mtime);
            
        }//while
    }//if
    closedir(dr);

Here's some sample output from my program. I'm focused mainly on the mtime of the file test.txt.

vagrant@vagrant:~/gios-spr-22-pr4$ ls --time-style='+%s' -l ./mnt/server
total 876
-rw-rw-r-- 1 vagrant vagrant 886443 1649448731 gt-einsteing2.jpg
drwxrwxr-x 2 vagrant vagrant   4096 1649535341 sample-files
-rw-rw-r-- 1 vagrant vagrant   1024 **1649535794 test.txt**


vagrant@vagrant:~/gios-spr-22-pr4$ ./bin/dfs-server-p1 
-- SYSINFO: DFSServerNode server listening on 0.0.0.0:42001
.. 1649616999 
**test.txt 1649535767** 
.gitignore 1648919848 
. 1649535767 

In short, why is ls and stat returning different mtimes for test.txt?

Thanks, Ben