[x0x0]

a breach is defined as

   ‘personal data breach’ means a breach of security leading to the accidental 
   or unlawful destruction, loss, alteration, unauthorised disclosure of, or 
   access to, personal data transmitted, stored or otherwise processed;

Given the definition, I think it's a bit hard to argue this isn't a breach. It's a breach of security leading to unauthorised disclosure or personal data.