"But the authorities say the attack is a sign that they have survived"
Boy, nothing gets past "the authorities."
Cargo cult gone wrong
First of all,the Indian CoastGuard helo was not on an aid mission.It was flying over the more remote & smaller islands in the Andaman chain to look for signs of the rare tribal groups living there.There were grave fears in India that many have been wiped out.But the firing of arrows & subsequent sightings of other groups has been taken with a big sigh of relief-infact the Coast Guard was gleefully annoucing that arrows were fired at them(usual tribal way to know that things are A-OK)!!!!.Moreover it is unlikely that these tribals need much aid ,if any,since their interaction with the outside world is very limited & the Indian goverment doesn't really want to change that for both socio-cultural,ecological & most importantly strategic reasons.
I know, that is so silly. I guess if they had all died, they'd be accepting help more graciously!