ground at the factory! Grinding won't affect the hardness which is why thats how they size them after hardening. And you can't size and THEN harden as hardening (whether its case hardening or whatever) tends to make things grow and loose parallelism.
I can't see how else they'd do it TBH (and case hardening wouldn't do it, wrong kind of loading)
Probably plough ground rather than on a flat bed grinder (or surface grinder if you prefer that terminology) but hardened and ground nontheless!