I think it's just a stylistic choice.

We may or may not have fought a holographic projection of Gaius, but the room in lore most certainly did not suddenly turn into a recreation of the conquest of Werlyt. Just as I doubt that at the end of 4.3, the interior of the Castrum suddenly turned into an autumnal Japanese garden.

If the recreation of Werlyt inside the Castrum happened in lore for real, then we effectively had introduced straight up holodeck technology into the setting, which has massive implications. I don't think that the G-Warrior training simulation from 5.3 counts, as I don't think that was an actual holodeck, but rather just the WoL sitting in the cockpit of the G-Warrior doing simulations but the G-Warrior is not actually moving and the landscape has not been altered or anything.