That's usually true that the OpsSpecs differ slightly from the regs, but from my experiences, the airline isn't looking for you to know what their OpsSpecs state. I don't have any personal knowledge of Horizon's interview process, but the airlines whose processes I do know, the interviewer wants to determine if you have a general understanding or a working knowledge of what the regs state and how they would be applied. They know that they'll need to train you on their specifics from the OpsSpecs, so they're checking to see if you have a solid foundation that they can build upon. Hopefully that helps you a little and maybe someone with Horizon-specific knowledge can provide more information.