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: