Aldrich witnessed the villains start the fight against Volantis the Bone Tyrant and watched only for a brief few minutes before his invisible Grave Ward was destroyed by collateral damage from Volantis's area of effect bone attacks.
That Volantis would appear here was a massive surprise. He was a level 40 boss character and the weakest among five Deathguard that formed the inner circle of powerful troops that served the Death Lord.
But even then, he usually guarded the 30th floor of the Necropolis, so to see him so early down in the 15th meant that the Death Lord fully intended on not allowing Aldrich to pass the 15th floor.
At the same time, Volantis only needed the villains to reduce him to half health and from an initial survey of his moves, it did not seem like he was using the full extent of his move set. This way, the encounter was 'balanced' enough that Aldrich could handle it provided he was around level 30.