India is trying to determine if China is supplying small arms and other weapons to Indian communist (Maoist) rebels. There's no doubt that the Maoists are getting Chinese made weapons. But there's also no doubt that most of the Chinese weapons getting to rebels around the world are sold by Chinese gangsters, not the Chinese government. But, of late, China has been acting more aggressively with India regarding border disputes. So it would make sense for the Chinese government to facilitate the Maoist rebels getting lots of Chinese weapons. Recent Chinese moves have made the Indians suspicious.
In the last few months, China has caused considerable consternation in India by reviving old claims. In northeast India, the state of Arunachal Pradesh has long been claimed as part of Tibet (although when Tibet was an independent nation a century ago, it agreed that Arunachal Pradesh was part of India.) Arunachal Pradesh has a population of about a million people, spread among 84,000 square kilometers of mountains and valleys. The Himalayan mountains, the tallest in the world, are the northern border of Arunachal Pradesh, and serve as the border, even if currently disputed, with China. This is a really remote part of the world, and neither China nor India want to go to war over the place. But the two countries did fight a short war, up in these mountains, in 1962. The Indians lost, and are determined not to lose if there is a rematch.
China also has claims on Kashmir, and actually occupies about 20 percent of the region, and claims the rest. Recently, China has been issuing special visas to Indians from Kashmir, who are travelling in China. This caused a diplomatic flap with India, which saw the special visas as a Chinese attempt to claim that Indians in Kashmir are, well, not really Indian.
China is tweaking the Indians as part of a campaign to negotiate a treaty to settle, once and for all, these many border disputes. India has been reluctant to give in much to the Chinese, and the issue is not seen, by either nation, as worth another war. So non-military pressure is being applied.