Difference in istio release artifact and the actual code

1.5.1 version on github has version and appVersion as 1.1.0 https://github.com/istio/istio/blob/9d07e185b0dd50e6fb1418caa4b4d879788807e3/install/kubernetes/helm/istio/Chart.yaml#L3:L4

But downloaded artifact has correct matching version

$ cat ~/Downloads/istio-1.5.1/install/kubernetes/helm/istio/Chart.yaml 
apiVersion: v1
name: istio
version: 1.5.1
appVersion: 1.5.1
tillerVersion: ">=2.7.2-0"

I have a jenkins job that downloads selected git tag, adds our customisation and package the helm chart, in that helm chart version is coming as 1.1.0 because of sourced github has non-matching version.

Does anyone know why is this difference?