Okay, here's my take on this based on what we know so far. It can change radically as the details get fleshed out as they inevitably will.
First, I wish Geno a speedy recovery.. for his own and for our sakes. And that LB should indeed have been cut on the spot which he was.
Given that, I think we can all agree, especially when it comes to testosterone-raging young men, that physically sticking one's finger in another's face invades their space and invites a reaction. That reaction may be deliberate, fueled by animosity or even a reflex reaction. Geno can never be considered in the right by doing that.
So this begs the question: did Geno goad the LB into this argument. Reports are that he's been confrontational to teammates on the field. We know that he suffers from this sense of entitlement, going back to his well-documented pre-draft attitude when visiting potential teams and of course, the pissy fit he threw in the draft room when not selected in the first round. Bottom-line, if his attitude provoked this confrontation, then coupled with the finger in the face, he actually got what he deserved. If not, then, extra sympathy for the hard-earned learning experience that as the QB and presumed leader of the team, you both turn the other cheek and conciliate and diffuse... rather than inflame and antagonize.