I did some digging and it looks like they were talking about https://tools.ietf.org/html/rfc6549 OSPFv2 Multi-Instance Extensions.
...
This document defines the OSPFv2 Instance ID to enable separate
OSPFv2 protocol instances on the same interface. Unlike OSPFv3 where
the Instance ID can be used for multiple purposes, such as putting
the same interface in multiple areas, the OSPFv2 Instance ID is
reserved for identifying protocol instances.
...
This document extends OSPFv2 with a mechanism to differentiate
packets for different instances sent and received on the same
interface. In support of this capability, a modified packet header
format with the Authentication Type field split into an Instance ID
and AuType.
...
This is not about Junos configuration tweak but a protocol implementation tweak.
As far as I know the only way to run multiple OSPF instances in Junos is to use routing instances. Since single interface cannot be configured under multiple routing instances there is no way to use this functionality in Junos.
Am I right?
Regards, Wojtek