My thoughts:
1. Epic talisman could have epic'd version of blood sacrifice spell for a brief time?
2. There was an exploit back in the days that let you carry 2*each exclusive item (buyback and dragging from bank while DC'ed), also prolly some exploit to fast-using it so this guy could just use 4*blood sacrifice (2*heroic, 2*epic) in no-time.
3. If he was pure arti it might be that Blood Sacrifice scaled with arti Arcanotechnician capstone to CL:20, and prolly this spell takes more HP giving more SP with CL upgraded. Also some levels with arti gives wondrous items up to +5 with it's CL.
4. EROSS, or ROSS with artificer wondous items/capstone, and he just removed his HP/CON ring to do that

5. Torc procing on some self-damaging skills/spells, and maybe this guy managed to self-damage for 1dmg but hundrets times. Maybe a vicious weapon, wearing 2 uncleansed GS, dunno.
Maybe we can excavate some old exploit out of it