Your initial placement on the Guild Wars leaderboard, was based on your total Guild Trophies at the time the leaderboard was populated.
After the first Guild Wars, when we actually had Guild Wars data, Guilds were moved on the leaderboard based on their Guild Wars score.
So, if a Guild had a very low amount of Trophies or had none, but did exceptionally well in Guild Wars, then it’s likely players will see a surge of movement.
Sirrian shared the calculations here