I don't think that Cameron went that far. When visiting Wales on 27 February he is quoted as saying that the UK government, "will
consider (
my emphasis) the case and options for devolving further powers to the Assembly over Air Passenger Duty (APD), informed by a review of potential options to mitigate the impacts of APD devolution on regional airports".
Live updates as David Cameron and Nick Clegg make new powers pledge for the National Assembly in Cardiff - Wales Online
My view is that unfettered devolution of APD powers to Wales would have been more likely with a Labour Government relying on the support of the SNP and Plaid Cymru, although that's not to say it won't happen with the new Conservative government.