2021 TOYOTA AVALON Tires Problems

Bridgestone Turanza EL440BW 235 45R18 94V is original equipment on my 2021 Toyota Avalon Hybrid. Mileage at the time of the incident was 11398. I saw what appeared to be splitting or separation of the lower depth of the tread. No loss of pressure. I brought it to the Toyota Dealer to check. They insisted I must have hit something and would not consider it a manufactures warranty. I replaced the tire out of safety concerns. I do not recall hitting or going over anything. I am attaching photos of the condition. I replaced the one tire with the same make and model but remain concerned that splitting of the tread could be dangerous. And still have 4 like tires on the car.