Yes, if he heard you he will be worried about you, but unlikely to confront you; the causes of somebody sobbing at the office can range from having a bad day to serious, personal issues that you wouldn't even ask your best friend about, much less your employee.
That being said, as long as you are certain there are no additional issues like depression, anxiety or burnout, then I wouldn't worry about it and just let it be water under the bridge. If it happens again, then I would suggest talking to your boss, but if it's a one-time thing just let it go.