The numerous attestations that Sanichar was the inspiration for Mowgli seem, for the most part, reference-less. One (in my opinion significant) piece of evidence to the contrary is Kipling's memoir Something of Myself, where he wrote:
My workroom in the Bliss Cottage was seven feet by eight, and from
December to April the snow lay level with its window-sill. It chanced
that I had written a tale about Indian Forestry work which included a boy
who had been brought up by wolves. In the stillness, and suspense, of the
winter of '92 some memory of the Masonic Lions of my childhood's
magazine, and a phrase in Haggard's Nada the Lily, combined with the echo
of this tale. After blocking out the main idea in my head, the pen took
charge, and I watched it begin to write stories about Mowgli and animals,
which later grew into the Jungle Books.
The Kipling Society has a well-researched follow-up on this passage, which offers a good number of useful details.
Kipling had already mentioned the 'Masonic Lions of my childhood’s magazine' in the first chapter of Something of Myself as part of his childhood reading: 'I came across a tale about a lion-hunter who fell among lions who were all Freemasons, and with them entered into a confederacy against some wicked baboons', which 'lay dormant until the Jungle Books began to be born'.
The allusion, traced by R. L. Green, is to James Greenwood’s story, “King Lion”, which was published in the Boy’s Own Magazine in 1864:
It tells of the hunter Linton Maberly who meets a lion suddenly when out shooting, and, having no time to reload his rifle, makes in a mad moment of terror `the ever potent sign known to all Freemasons’, and, to his astonishment, the lion ‘made the dread COUNTER-SIGN known only to those who have passed through the Three Degrees of the mystic order’. The lion, Prince Zambanie, son of King Lion, befriends Maberly, teaches him the Lion language, and conducts him to the leonine court at Liondens. On the way occurs the brush with the Baboons which culminates in the concerted attack by the Lions on the baboon stronghold, and the defeat and chastisement of these rebellious subjects of King Lion.’
Nada the Lily, H. Rider Haggard’s romance, published in 1892, relates an episode in the career of Umslopogaas, one of the heroes of Haggard’s Alan Quatermain. In the course of the story, Umslopogaas is rescued from a lioness by Galazi the Wolf. Galazi tells Umslopogaas how he became King of the Wolves; these wolves are ghost-wolves, encountered by Galazi on Ghost Mountain. Galazi describes finding the skeleton of a man sitting on a ledge of rock inside a cave, with two wolves, one female and one male, forever leaping up at it, trying to get at the bones; and it was specifically from this passage, Kipling wrote to Haggard, that he `got the notion’.
We see that Kipling himself didn't explicitly include Sanichar as an inspiration for the character or the idea. No author, of course, works in a vacuum—and Kipling never claimed to—so it's of course possible that Kipling was somehow indirectly influenced by various accounts of such 'feral children'; there is nothing in the direct evidence, however, nothing in the paper trail, that would definitively prove so.