wallah does indeed mean 'By God!' in arabic but it's used as an assertion of veracity. In this context the poster obviously meant to say voila and like you I've also seen this wallah variation of it creeping in recently.
Retro-validation appeals to me, so it could be interpreted as:
and - truly, I swear by God I am not making this up - I was granted a ticket with that exit row seat
In English, it's an old-fashioned idiom that a Robert Louis Stevenson character might have used. But English-speakers tend not to swear by God much these days - indeed, "swearing" usually means profanity.
