(Not an official answer, I'm just a regular user)
The ranking is a function of votes, flags, and time. Not all votes are equal, as some votes are determined to be correlated via voting-ring type considerations.
But if a submission gets four or five independent votes very shortly after submission then it can easily make the Front Page. It won't happen if the votes trigger the voting-ring detector, or if the submission is flagged by someone.
Why do you ask? Why are you surprised? What other reading have you done before asking the question?