It seems that on macOS some manual work must be done to allow run program to run an app bundle when the installer is completed. Here is the script I'm using:

function Component()
{
    installer.installationFinished.connect(this, function() {
        if (systemInfo.productType === 'osx') {
            installer.setValue("RunProgram", "/usr/bin/open");
            installer.setValue("RunProgramArguments", "@TargetDir@/bin/at-browser.app");
        }
    });
}

It would probably be better for Qt Installer Framework to handle this situation automatically, the solution was not obvious to me. Sorry if I missed something