It is most unlikely to be Jet2. If Lufthansa have made this announcement then Jet2 (well, Dart Group PLC) would at best be in breach of good practice and at worst potentially in breach of market regulations if it failed to make some corresponding statement of its own.
The clues are in the Lufthansa statement. It has not granted exclusivity to the bmibaby buyer which means either a) it's not happy with the deal or b) that it isn't confident that the buyer can actually complete, or c) both. Best guess is that if this is a UK organisation, it's the management team who haven't yet got funding to support their buyout.