Were there a lot of people at the lecture?

W: Did a lot of people attend the lecture?
M: Well, yes and no.
W: What do you mean?
M: You see, the classroom was quite full at the beginning. Almost all the seats were occupied. But after the short rest, almost one-third of the audience left.
W: Terrible! That was a very rude thing. I should have been there. I had told the students to behave themselves. I do hope Professor Black was not angry.
M: What do you mean? He wasn’t even there.
W: What? Professor Black did not come?
M: No, his lecture is Thursday next week, not this Thursday.
W: Oh, yes, of course. How silly of me!