Why does os.listdir() sometimes contain files that are no longer in the directory?

I looking for a conceptual understanding of os.listdir(). I used os.listdir() to iterate through each file in my directory, however, a filename in os.listdir() was not in the directory. This is the error I experienced:

FileNotFoundError: [Errno 2] No such file or directory: 'a29ydW5pc2hpLnR0Zg==.png'

After further inspection, I discovered this stack overflow entry: List files ONLY in the current directory

Because of this page, I suspect that the filenames in os.listdir() may not match the ones currently in the directory. I came to this conclusion because of os.path.isfile() documentation suggests that sometimes extra file names might still be in os.listdir().

Why does os.listdir() still contain entries of files that are no longer in the directory or why is this filename in os.listdir() when it isn't in my directory?