The Great Gatsby, chance visitors

Could you please tell me the meaning of "chance visitors" in the following excerpt from the last chapter of The Great Gatsby? Does it mean "visitors who came by accident" or "for the occasion"?

I went back to the drawing room and thought for an instant that they were chance visitors, all these official people who suddenly filled it. But as they drew back the sheet and looked at Gatsby with unmoved eyes, his protest continued in my brain.

Thank you.