Process history showing actor name as Administrator

Yeah thats true. It does not specify anything related to the role of the person or anything but not able to understand where this administrator is coming from

I observed one pattern where administrator name comes up when subprocess is triggered which is present in a workflow. More like a task is present in the flow and when its completed, the subprocess is triggered

The value will be different depending on how the top-most parent process was triggered as well as what the "Assignment" configuration for the subprocess is set to.  If the subprocess is set to "Run as whoever designed this process model", then regardless of the initiator of the parent process, the initiator of the subprocess will show up as whatever account last published the subprocess (typically your Import Admin service account, assuming you're hopefully using such a setup).  If it's set to "run as whoever started the process", then it'll inherit the "initiator" value from its parent (NOTE: it can only inherit the exact same "initiator" as the parent, there's no avenue by which to change this to any other user).

There are a couple of places I've seen "Administrator" come up.

• If the process model is a feature that is installed by Appian Support (e.g. RWM / RPA, Case Management, Process HQ) or it is a process model that was installed by Appian when creating your environments (which happens on beta environments), and that process model is set to "Run as whoever designed this process", then "Administrator" will be the process initiator. This can also happen if Appian Cloud Support republishes existing process models for whatever reason, but there would be a support case tied to it.
• It's been a while, but I also vaguely remember some nuance about pp!initiator when the process was started by process to process message receipt.
• if the process were started by email, you should see ANONYMOUS (as of 24.2).
• The only other place I've seen "Administrator" is when checking the box to automatically create Appian users during SAML authentication. The audit logs will show "Administrator" as the account which created the user.