There are several date systems followed by different tools. The most common one (used by excel as well) is the one called:
The 1900 Date System
In the 1900 date system, the first day that is supported is January 1, 1900. When you enter a date, the date is converted into a serial number that represents the number of elapsed days since January 1, 1900. For example, if you enter July 5, 1998, Microsoft Excel converts the date to the serial number 35981.
Qlikview uses 1900 Date System. Hence the number you see.