This story is so full of holes it only made the 'news' because it advances the 'China threat' position so many in the west loves to advocate.
Firstly, as Steelbird has already pointed out, this is an Indian Navy warship, which is supposed to have radar, but they saw no sign of a Chinese ship or aircraft, so the only basis for thinking this was actually the PLAN is because the guy on the other end of the radio said he was the 'Chinese navy'.
Secondly, if the Indians could not see any sign of a PLAN ship or plane, and presumably this ship would have had the EW gear to know if they have been painted by another radar, how the hell did the 'Chinese navy' know where this IN ship was?
It could have been a sub, but a sub raising its mast to broadcast would surely have been spotted on radar. Besides, subs would not go and challenge a foreign warship directly like that, the most they would do is call the incident in if the Indians really did stray into Chinese waters and shadow them while a surface ship or air asset can be brought in to challenge them.
Thirdly, if this really was the PLAN, they would not just make a challenge and then not follow up on it if the Indians failed to respond.
This just sounds like a prank call by some kids with a radio, probably from Vietnam as well.
Looking at the facts as presented, this just strikes me as a very poorly handled situation by the Indian Navy if anything.
It is surprising that in this day and age, a frontline IN warship does not have the EW gear to get a bearing of where an open frequency transmission came from.
The way the Indian Navy handled the incident is also pretty sloppy. If they took this challenge seriously, then they should have tried to locate where this challenge came from and answer it instead of just wondering off with no reply or action. What if there was actually a PLAN ship or plane that was challenging them? As I mentioned earlier, they would not just make a challenge and do nothing when the Indians fails to response. The failure to respond on the part of the Indian ship could easily escalate the situation as the PLAN might seek to use stronger measures to get them to respond.
OTOH, if it was blatantly obvious that this caller who claimed to be the 'Chinese navy' was not following expected protocols and looked to be a hoax call, why make such a meal of this non-issue? It just serves to make the Indians look foolish for taking it so seriously, and these obvious questions and implications that that FT reporter should have been asking before writing up that copy and paste piece is probably why the Indian navy seems to be now denying that this incident even took place. As no matter how you cut it, the Indians come out looking bad.
It really is a bit of an own goal for the Indians, as they should have just chalked this off as a prank call and not even mentioned it at all.