Well there have been larger casualties before
en.wikipedia.org
4 June 2015, guerrillas ambushed a military convoy in
Chandel district,
killing 18 soldiers and wounding 15 others. UNLFW claimed responsibility for the attack.
[18]
22 May 2016, militants ambushed and
killed six Indian paramilitary soldiers in Manipur, India near the northeastern region bordering Myanmar.
[23]
Chinese may not be involved , RDX for the IED is used for blasting in quarries . could have been stolen or brought illegally.
if the chinese are involved , maybe India will do another bus attack in POK .
below is IED that was discovered.
check the arrow , i think thats the direction IED should be facing the vehicle
also check the color , same as the color of bus in dasu bombing which killed 18 chinese engineers