My significant other was also on this flight and filed a claim. His claim was also denied, but for an entirely different reason:

"We’re sorry it was necessary to delay your flight from St. Lucia on 28 April 2024 and understand why you needed to get in contact about this. We take all reasonable measures to avoid delaying a flight and we’ll always consider if there are any alternative solutions available before we make a decision. We'd also like to thank you for your patience while we got back to you about this.

Your claim's been refused because BA2158 on 28 April 2024 was delayed due to Air Traffic Control restrictions. The delay was out of our control and caused unforeseen disruption to our schedule.

We're happy to reimburse your other expenses. So that I can look into your case further, please send us an itemised list and receipts of your out-of-pocket expenses. Your itemised list should include the name, type and the individual cost of the items with correct currency code.

Once again, please accept our apologies for your experience on this trip. We hope to welcome you back on board soon.

Best regards

Prajakta
British Airways Customer Relations"