I think, It was indeed another rumour (like lord ganesh idols)dat spread across Mumbai.
I think it is because of the copius amount of fresh water (rain water) that has been added into the sea, which made the sea water taste SWEETER.
The rumour could also be purposely made by some terrorist group (taking advantage of the natural phenomenon) to make people throng a particular area to make it as a target location to carry out their exercise. Luckily nothing happened, my view is that its always better to tighten the security to places where more people gathers together, regardless of the cause for such a gathering.
