Don't worry, you WILL KNOW when you have a dry socket, they are very very painful indeed. It was probably a clot, but not the clot that is in the socket (up further) that would cause a dry socket. just keep on doing what you were told by your dentist, or oral surgeon and you will be fine. Good luck.
shinty
It may be some food debris mixed with blood that came out. As shinty stated, a dry socket is usually quite painful and would need to be "packed" with placed with a dressing.