I am a bit confused here, is this the case of a last minute change or is this pretty common?

Detailed Flight Information
Flight LH416
Departs 10:15 on Wed 25 Oct
Frankfurt, Frankfurt Int'l, Terminal 1
Arrives 13:05 on Wed 25 Oct
Washington, Dulles Int'l, Terminal
Duration 8h50
Airline Lufthansa
Aircraft Airbus Industrie A330-300

I was really surprised when offered seat 2K. I was totally expecting a 747 with old C.

Any past experiences guys?