What part of ERPNext is GPL'd, if not the core?
All of it.
I think rushabh's point was that the Odoo model is an open source core with closed source paid components, whereas ERPNext is fully GPL'd.
ERPNext monetize via a SaaS model, but you are free to self-host.
ERPNext is not open core like Odoo.
Disclaimer: I am the founder of ERPNext