Whew!
Many of those I've seen had 10-3 without ground, too. Either way is correct.
That's still wrong. A sub-panel is like a mobile-home service, which has required major appliances on 4-wire circuits for many years.
I disagree if fed from a subpanel, it would have required a insulated neutral & when it was allowed for new installations a 3-wire receptacle would have been code compliant.