tl;dr fe8 does things differently than fe7
While in FE7, you have the table pointer array that tells the game how many PC units there are and where they are; and then a pointer to the enemy group visible during prep screen.
In FE8, these are actually mapped to Easy/Normal and Difficult mode deployment slots for the player. So while it's still being figured out, this is basically just the event pointer table's basic functionalities being futzed with. The "glitch" shown there is just what happens if you put all the enemies in the same UNIT list as the player units while you have a prep screen on the chapter.
The "glitch" just lets you swap player units with enemy units, though it only lets you move enemies if you select a player first.
This makes the current status of the chapter pointer table look like this:
POIN Dunno1 Dunno2 Dunno3 //AFter EVent data (?)
POIN TrapData DifficultModeExtraTrapData
POIN PlayerUnitsEasyNormal PlayerUnitsDifficult
POIN $0 $0 $0 $0 $0 $0 //Skirmish data
POIN BeginningScene EndingScene
And I want to finish populating it out, so I've been futzing with it and that glitch came around when I was doing so.