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.

It is still a common idiom in US English.

Further evidence that this person is not a native English speaker! ;)

My parents are Middle Eastern Jews from Iran and Iraq and my understanding of their use of wallah is to mean "for real?" or "surprisingly so!"

Yes it means that too but deriving from the sense I mentioned, i.e. asking if the person making the assertion would swear to it 'by God'.

The French pronunciation of voila is akin to "fwalla", with the f/v sound being relatively subtle. At any rate it's not as amusing as misspelling it as viola.