IIRC, WPARs could be just for one process, or full OS (but sharing the resources of one AIX instance, I guess that running on an LPAR or directly in the hardware).

But yeah, bit more like a container.

Then it was probably an LPAR. Are those reliant on hardware magic or just something like cgroups?

LPARs use hardware virtualization. The PowerVM hypervisor (PHYP) is in firmware.