Is the attack against the attacking psyker classified as a psychic power in terms of:

Can the attacking psyker use Resistance (Psychic Powers) vs the attack?

Can the attacking psyker use his own Mental Fortress to attack back? Possibly causing an endless rebound loop until someone dies?

The book states it's an impact attack. I assume it means it's a telekinetic attack vs the individuals head making him unable to use Strong Minded vs the attack.

A character with Mental Fortress has learned various mind defense techniques that can trip up and actively harm a psyker trying to use their powers against the character. The damage from the Talent is not itself a psychic attack (the character doesn't have to be a psyker themselves) but more a psychic backlash against the attack. So it wouldn't trigger the psykers own Mental Fortress or Strong Minded talents and cause an infitie loop.

Ahh.. excellent, thanks for your reply.