Can you provide another picture like the second one but with the cover of the way showing the stub of the cut off cord? Also you probably dont know why the cord was removed. Since they just cut it, it was probably just some last minute salvaging, but its possibly there was a problem with the transfer switch or it may have some other electrical issue down stream.
So before you install the new cord, turn off all the 120v breakers. When you plug in you should hear a noticable “thunk” when power transfers. Then do a quick verification with a multi-meter, ensuring power is being fed to the panel leads, then turn on your breakers one at a time, and test each component to make sure there are no issues with it. This way you can verify there are no issues with each item rather than trying to trouble shoot the whole rig later.
Hopefully there are no issues, and someone just needed/wanted a free extra cord. But you wont know until you test the whole system and this is something you dont want to discover in a campground miles from home. Good luck - hope it all works out.