It's very likely. I looked up CXP8318, And it's a ICAO, which means that plane was in service. However, we do know that Xtra Airways have 6 737-400, so it could be one of the six.
Until we can find out what FAA registration number was on that aircraft, we will consider that as an assumption.
One I will point out is that it's been 21 days since the last 8K informing that an aircraft would be undergoing a C-check. It normally takes 2-3 weeks to do it. I do see the timeline lining up quite well to indicate that it could be the N417XA aircraft.
So, I'll remain at "Likely," until new information is presented.
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