Well you can call it nonsense , but this is infact the most popular theory on origin of Hazara people . In history , there are theories , not verdicts
Another popular theory proposes that Hazara are descendants of the Kushans, the ancient dwellers of Afghanistan who are believed to have built the Buddhas of Bamiyan. Its proponents find the location of the Hazara homeland, and the similarity in facial features of Hazara with those on frescoes and Buddha's statues in Bamiyan, suggestive. However, this belief is contrary not only to the fact that the Kushans were Tocharians, but also to historical records which mention that in a particularly bloody battle around Bamiyan, Genghis Khan's grandson, Mutugen, was killed, and he allegedly ordered Bamiyan to be destroyed in retribution.
. The theory, and the one accepted by most scholars, however, is that Hazara are a mixed group. This is not entirely inconsistent with descent from Mongol military forces. For example, Nikudari Mongols settled in eastern Persia and mixed with native populations who spoke Persian. A second wave of mostly Chagatai Mongols came from Central Asia and were followed by other Mongolic groups, associated with the Ilkhanate and the Timurids, all of whom settled in Hazarajat and mixed with the local, mostly Persian-speaking population, forming a distinct group
Hazara people - Wikipedia, the free encyclopedia
Without taking side in this controversy (see also Ferdinand, 1959, 1964; Mousavi, pp. 28-31), it seems probable historically that the origins of the Hazāras lie with the Mongolian and Turkish groups which progressively penetrated the infertile mountainous region situated between Persia, Central Asia, and India between the 13th and the 15th centuries,
mixed with the local population and adopted their language. It must also be pointed out that Turko-Mongolian people, like the Hephtalites (5th and 6th centuries), were already present in what is today Afghanistan and therefore may also have played a role in the ethnogenesis of the Hazāras (Mousavi, p. 38).
Nevertheless, Fredrik Barth’s work on ethnicity (1969) has made it evident that group identity is not defined by objective traits and does not follow from a common origin or even a common culture. It is, rather, the result of a constant process of social interaction by which a boundary is created and maintained in an enduring way. There are many Middle Eastern examples where distinct groups were formed by people of heterogeneous origins in marginal regions following a continuing process of inclusion and exclusion and of resistance to central powers (Canfield, 1973a, pp. 10-12 and 1973b, pp. 1511-13).
In the case of the Hazāras, the feeling of belonging to one group does not proceed from a supposed Mongolian origin, but from a process of marginalization which started several centuries ago. As mentioned already, the term hazārahas been used to designate a heterogeneous group, including some Sunni groups (for instance in the district of Rustāq, province of Taḵar, or the district of Nahrin, province of Baḡlān). It seems to refer as much to a social position as to a common historical origin.