Baseboard chip what can cause damage to it?

I’ve sold a phone for spares and repairs on eBay. In the title and four other places this is how the condition is described. It sold, I posted it but now the buyer has put out a refund request.

Apple have told him the baseboard chip has blown and that that can only happen through water damage. When I was hoping to repair the phone myself I wasn’t told this sort of information from Apple.

I want to know if this is true. This phone had a case on and has NOT been submerged.