I can't see the BBC news article you mention, unless you are reading an article from a few weeks ago?
All today's announcement is, is confirmation of an order that was already announced at the Dubai Air Show in November, and is part of an order for 430 A320/321neo's, and 146 of those aircraft are allocated to Wizz...
The order has come from investment company Indigo Partners, who are a major shareholder in Wizz Air and also hold major shares in airlines in the USA, Mexico and Chile, which are all managed independently. Indigo are funding the aircraft order and by buy ordering in bulk for all three airlines they have negotiated a huge discount from Airbus.
(The allocation according to Wikipedia is, 146 aircraft will go to Wizz, 134 to Frontier, 80 to Volaris and 70 to JetSmart.)
Today's announcement is just the signing of the paper work and firm commitment, and going by what I am reading Airbus have pressed for the confirmation of the order by the end of the year. I think this is due to Airbus not having the most successful of years with regards to orders compared to arch rival Boeing and want this big order to bolster their order book and steal headlines from Boeing.
With regards to Luton expansion this was announced about a week before Christmas and Wizz have purchased all of Monarch's slots, which will increase their base from three to seven aircraft. New routes announced included Bari, Athens, Reykjavik, Lviv and increases in frequencies to other routes including Tel Aviv and Larnaca.