Your assumption is almost certainly correct. Century Arms' modus operandi has been for decades to purchase large batches of surplus foreign service weapons and import (or re-import) them to the US civilian market.

Their business model has been built on the fact that most other countries, due to restrictions on private gun rights, have no profitable market for their own no longer needed issue guns, and are willing to give them cheaply to someone offering to take them off their hands.

So Century has always been a volume buyer and generally wouldn't deal in private used guns, making your MR 73 most likely a former service gun and part of a batch buy.