Because .NET is an additive package. .NET 3.5 for example doesn't replace any other .NET version (except another release of .NET 3.5), it just installs alongside other .NET packages.
.NET 4.5, 4.5.1, 4.5.2 and later all include all versions of .NET 4.0. Apparently QlikView only uses .NET 4.0.3, nothing from the more recent stuff.
You can check this out in the registry yourself by launching regedit and navigating to key HKLM\SOFTWARE\Microsoft\.NETFramework. There you'll probably find two major versions, v2.0.xxx and v4.0.xxx. Expand the v4.0.xxx\SKUs tree and it'll show you which .NET versions are available on your platform.