When I kick off a build using jenkins-cli.jar, the causes element is as follows:

"causes": [
{
"shortDescription": "Started by command line by kallan"
}
]

When I kick off the same build from the web UI, I have access to more information:

"causes": [
{
"shortDescription": "Started by user Kyle Allan",
"userId": "kallan",
"userName": "Kyle Allan"
}
]

When Jenkins is working in conjunction with: Email-ext Plugin, version 2.22, this is not enough information to trigger the code to send an email to 'Requestors' (the individual who kicks off the build). The relevant code for this logic can be found in https://github.com/jenkinsci/email-ext-plugin/blob/master/src/main/java/hudson/plugins/emailext/ExtendedEmailPublisher.java#L463