Because trolls like to call out people's BS. Trolls lack reading comprehension and just want to start a fight.
This seemed pretty obvious to me. Mind you the reason why is because I've manually controlled 2 or 3 players of a 4 player party on another game before using 3 separate machines, and it's simply not possible to do this unless one of the characters is basically being a packmule to pick up extra loot. Humans are not built to multitask.
Here's how you roughly tell:
Separate people controlling separate accounts - They react with different response times, and move independently.
One person with several accounts on different machines - They alternate between movements/commands, and move in straight lines. Using key-repeating software also allows one to play several characters of the same class/job.
One person with several accounts from the same machine - One character will move, and then another will, but they will move sluggishly or rubberband, often in straight lines. Often requires all the alternates to be the same class/job from key-repeating software.
One person with several accounts from the same machine in VM/scripting/botting - One character will move like a normal player, and the other characters will operate independently, but won't talk in the party chat at the same time, if they die, they don't ask for help.
The tells for automation often include low-efficiency dungeon running (eg pulling one monster at a time) and being unaware of the surroundings, or "scripted" surroundings:
1) Bots frequently jump into walls/obstructions because their "follow" master gets too far away.
2) Bots run to known objects in the dungeon (eg chests), even when open
3) Standing in AOE's/traps
4) Spamming Sleep
5) Wearing inappropriate gear (Harvesting bots and Spirit-bonding bots are VERY easy to tell because of this, they often have missing right-hand-side gear or dungeon-trash for gear)