I am not sure what the broker is doing here but it seems clear that you need double check this sqft #.
Even liberal addition from the layout shows:
Basement: 1600
Ground Floor: 2300
Second floor: 1200
Third Floor: 1000
Total: 6,100 sqft including the basement max (4,500 w/o the basement)
If you add in the terrace space at 50% you get almost exactly 6,700. What kind of math is this?
Description should read: 4,500 sqft townhouse with finished basement and huge terrace.