It appears that the frag got too hot in the box. Using a heat pack when the destination location is going to be in the 80's probably isn't the best plan. I've received shipments that were too cool and the acros had lost color but we're alive and able to recover. I received an order in July 2019 in Oklahoma with temps around 100, the vendor didn't use an ice pack, and this was the result:
Looks just like the OP's frag. It appears that the seller thinks he should be 100% whole in this transaction and the buyer should get nothing but a discount on another order. There's no way I would try another transaction with this seller. It appears he's "learning" and that his buyers have to suffer during his learning curve.
IMO the shipping delay didn't kill this coral. The heat pack most likely did. My above-referenced order was received on time but a total loss due to the heat. In my case the vendor replaced the frags with me paying shipping.
While I sympathize with the seller trying to make a living, I'm sure his buyers work for their money too. Refunding the cost of the frag is the only resolution that's fair to both parties. The seller lost a frag and the buyer loses the shipping cost. Seems simple to me.