is almost certainly a simple error on the part of the person assembling the components for manufacture, so let's be charitable for the moment and assume that to be the case.
The alternative is to think that the processor change was deliberate, and the consequences of that would be very serious for any computer manufacturer - it's fraud. We have absolutely no grounds for believeng that to be the case however, and in the circumstances I advise you to wait for your machine to be returned. It's a simple task to check the components, and you'll probably want to do that to reassure yourself. If you need any help with that process post back here, and one of us will help.