Just a coincidence. Once the drives remapped the bad sectors, they were no longer accessed when doing full writes/scans of the disk (Is the total number of reallocated sectors still the same for both drives?).
Also, drives tend to fail in batches. If you bought both samsung drives at the same time/same store, there's a high likelihood that they came from the same lot of drives and share any manufacturing defects that affect that lot. (This is why you should change up brands or distributers when building RAID arrays - That way when one drive fails, you reduce the risk of losing a second to the same defect during the rebuild)