Probably superficial, but likely to get worse fairly rapidly.
As I understand it, the rubber chains under tension at the base of the crack get "snipped" by ozone attack, causing rapid crack propagation.
I tried vegetable oil as a protectant for 8 -year old tyres that looked fairly bad (though not as bad as that) before I treated them, maybe 3 years ago. Now they look better, but are probably due for another application.
That's too risky to suggest, but perhaps a less "homemade" treatment, like, IIRC, "Aerospace 303" might be worth applying, if you can't get a refund or exchange?