Great question @Michael Wills! I think both are considered subagents, whether if it's parallel nodes or a tool call. What matters is what's inside.
I could create a new agent instance inside a node block or inside a tool call function, the main agent won't know either way.
This new topic "Agent system design" is a new territory, and I'm sure there will be books about it in a couple of years and It's really great to witness this (Unless AGI annihilates us all 💥)
So, I think what dictates what makes a sub agent a sub..agent is not clearly defined.
In this repo for example a subagent is an agent without any previous context. And that's the beauty of it, if the lead agents deployed a sub agent to the 51st time that agent no. 51 won't know what happened before it and what his peers are working on (Other subagents).
All it knows, is that it's on an ephemeral mission, from and to the ether it goes, unaware of the grand scheme of things 😌
But please let me know what you think.