I'm going to break ranks here and point out this is a serious failure by British Airways, and 30K Avios is derisory. Think of yourself writing a letter of explanation: "During the cleaning process between flights, a contract employee failed to notice the presence of broken glass in the seat.". There's no way you can spin this that doesn't make it negligent, either in the cleaning process or the supervision, and the result is an injury to a passenger that drew blood which is fairly serious. Presumably if there was glass there was an incident which broke glass, and there should have been special care taken on the turnaround. Beyond that, there should have been an accident report and some sort of corrective action with the passenger kept informed throughout, rather than a three month administrative silence. "Our first priority is safety" doesn't stop at emergency procedures and evacuations, it does also mean protecting passengers from preventable accidents in the cabin.
I think the request is pretty reasonable to be honest, as the alternative could be litigation and reputational damage. A quick and generous gesture can stop a lot of the sort of bad will that persuades people it's worth legal action so they can "win" against an unresponsive company, and that gives time to work on finding the root cause of the safety issue and addressing it. Not all F seats are full, and the cost to BA of giving a couple is low, but that's not really the point.