FOM surely own the rights to any ‘official’ F1 running, be that race weekend or testing? After all, we have seen pre-season testing footage used on FOM’s official season reviews in the past, so it makes sense that they’ll have crews there to record some footage in case they have a reason to use it, whether for montages or for the season review DVD or any other packages they want to make.
Presumably if that’s true, Sky’s deal gives them the rights to show that footage. It may or may not be something exclusive to their contract though, I wouldn’t know.