So chinese are no threat at all?
Not unless they come as a large invading force. The himalayas prevents any large troop movements. Small patrols are not a threat, because we don't expect them to actually engage in combat. Nor do we expect them to support any terrorist activity within India by infiltrating secretly.
You have to remember, a lot of troublemakers have infiltrated into India though the Indo-pak border. A small group of pakistani soldiers who intrude can do a lot of damage, by providing cover for infiltrators, or by conducting reconnaisance for infiltrators, or by firing at our soldiers or....there are many possibilities. Indian and pakistani soldiers have fired at each other from time to time, a few soldiers on either side occasionally die due to firing or shelling from across the border. None of this is true about the Indo-China border. Soldiers don't do unprovoked firing, they don't help infiltrators sneak in. The relations are very very different.