Hi, Yes you deck was altered.
As far as I know, every B&O deck comes with DIN plugs and the 400x series for sure.
On the picture from Craigslist you can see it’s actually a DIN plug with a DIN to RCA adapter (note the two DINs one inside the other).
If you need to put it back to original you should find wiring diagrams quite easily.
If RCAs are good to you, the same diagram can help you check they’ve been wired correctly.