I can look at a job header (e.g. /blue/organizations/.../detail/master/102/pipeline) and see this:

If I click: 

I'm taken to /job/.../master/102

Which shows "Started by user" (core/src/main/resources/hudson/model/Cause/UserCause/description.properties: started_by_user)

Note: I don't really need this for "push event to branch" as that is the reason.

This appears to be:

https://github.com/jenkinsci/workflow-cps-plugin/blob/9b768a42f60cc3389031646c24927fa062d444e1/src/main/resources/org/jenkinsci/plugins/workflow/cps/replay/Messages.properties#L4