Oops... I got it. The sword was found by a non-archaeologist (one of the authors - R. Ramesh) at the bottom of some "pit" without any research of this pit itself or the accompanying material (we were only told about "an urn enclosed with a capstone"). But since the megalithic burials in this area "dated to the sixth century BCE or earlier" so this pit was dated to 6th century BCE too
. How graceful.
The article does not meet the standards of scientific archaeological research, although one of the authors (K. Rajan) is a respected archaeologist. Just pit, just sword, just an archaeologist-enthusiast, but as result we have the oldest sword made of wootz.
Just very sad. Hope I am wrong.