why is Mr. Dussel surprised to find the Frank family living in the annex?

Mr. Dussel was told the Franks had escaped to Switzerland.

You’re not in Switzerland, then? A woman told me . . . She said she’d gone to your house . . . the door was open, everything was in disorder, dishes in the sink. She said she found a piece of paper in the wastebasket with an address scribbled on it . . . an address in Zurich. She said you must have escaped to Zurich.