In biological, that is evolutionary, terms; genius is an altruistic trait.
This means that - on average, in the environment where and when genius evolved, being a genius will tend to reduce the genius's own personal reproductive success, while substantially enhancing the reproductive success of the group of which the genius is a member.
Biological altruism does not (or not necessarily) correspond with social altruism, or an altruistic personality- i.e. 'helping people' - because the genius's contribution to his community is via his work.
Indeed, it is characteristic of the behaviour of a genius that he will protect the conditions necessary for his work, even when this goes against usual and expected socially altruistic behaviour.
The genius may therefore be solitary - may indeed be selfish, may not marry or have a family, may not be a good neighbour. But selfish not really for his own benefit - not for money or status - but primarily for the work: selfish to enable him better to do (or to do at all) what it is he does.
Some geniuses are nice, some are nasty - that is not the point; the point is that the genius feels his first (or a very high) responsibility is to do his utmost to create and sustain the best conditions he needs for his work.
Thus it is quite possible, quite normal, for biological altruism at the group level to go with personal selfishness; and for personal un-selfishness to be anti-altruistic, and to damage the reporductive interests of the group.
Altruism and being nice: two very different things.