The only good news out of the bad news of the Milwaukee massacre at a Sikh Temple for sure is that the shooter was discharged from the Army with less than honorable, as to at least the Army having identified a problem, and therefore something Indians in general should draw some comfort from as to Americans not generally speaking be hostile to Indians in any sense that is more meaningful here than anywhere else.
The only other good news that could come out of the shooting is that people in America might understand the Sikhs better, beyond them not just being Muslims (often assumed because of the turban and beards male Sikhs are supposed to wear), a correct complaint of Sikhs and Indians in general.
That is the case even if there is much more complexity in the idea of the Sikhs not being Muslims too, from the point of view of comparative religions, a field which intersects to a large extent with comparative politics properly done, since religion is an important motivator of political conduct.
As to the origins of the Sikh religion, on the surface they clearly are not Muslims, since the first revelatory experience of the Guru Nanak was to say "Not Muslim, not Hindu."
And yet, the influence of Islam and Hinduism on the Sikh religion in the field of comparative religion is widely accepted as an example of religious syncretism, syncretism being mixing and matching, and common particularly in very diverse religious environments like India, where the Sikhs originiated in the 1400s.
As to gurus, at some level it has some similarity to the Shia branch of the Islamic faith as to Imams, if the Sikhs are very different as to generally not ascribing the same importance to clergy as do the Shia, although influence would be expected in terms of geography and therefore flow of ideas.
Where the Sikhs originated in the Punjab in India in general is the major intersection of course of Islam and Hinduism, in which if there has always been conflict, not only has there been cooperation, but also mutual adaptation too.
One can see that mutual influence in the art of the Mughals, and prior to that the nature of the Sikh religion.
The Sikhs are like Muslims as to monotheism and many prohibitions not found in Hinduism, but, besides denying the claims of universality of Muhammad's vision, their conception of things and especially the intensive use of meditation clearly have a Hindu origin, as to someone being able to say Sikhs are not Muslims or Hindus, but also both in many ways, if therefore also their own universe of religious practice too.
As to the most important significance of the Sikhs, it is in its geography as to the Punjab within India.
The Sikhs had their own kingdom in the Punjab until the 1830s, when the British of course conquered and coopted them like so many others, in the Sikh case, identifying them as a "martial race."
In that characterization, one can see more religious syncretism, as to the struggle the Sikhs are supposed to wage against Darkness, and symbolized by their famous swords they are technically supposed to wear, as to Iranianian influence dating to pre-Christian Zorastrianism, the latter itself a significant influence on Christianity too.
As to the Sikhs place within the religious world, in addition to Hindu, and indirectly Budhist practice, one can also again see Islam in the form of Sufism, the latter the mystical side of Islam not much liked in conservative Muslim quarters ever, if very common in Afghanistan and Central Asia.
So the Sikhs come from the crossroads of religion, and are therefore much more than Muslims, as also bearers of a martial and political tradition as well that has at times played out with some violence in India, if not usually.
There was a Sikh separatist movement that led to the "Second Amritsar Massacre" in Operation Blue Star in 1984, which was met with retaliation in the form of the death of Indira Gandhi at the hands of the Sikh bodyguards she refused to dismiss: martial race.
So if someone shot up a Sikh Temple because they thought they were Muslims, not only were they an idiot, but also unfortunately missed a much more interesting story as to the nature of religion in the world we live in, if that is of course so tragically often usually the case.