Logically speaking,
Matthew had to exert significant effort to summon undead from the material world or the negative energy plane to Storluk Planet.
At least, there was absolutely no time for him to set up the Star Realm Portal just after the battle had ended.
But Matthew had the Sampan Plane in his hands!
This plane was like a sampan that could travel back and forth between the material world and the astral world!
After the Great Tear,
the Sampan Plane was not damaged but instead became even more "soulful" after losing its restraints.
Matthew was able to greatly control the direction of the Sampan Plane through the Eight Extreme Celestial Instrument and the Wings of Wind.
This was precisely why.
He used that plane as a super springboard to transport military forces from the material world to the astral world.
In one fell swoop, he gathered over fifty thousand undead!