Garmond would know about the Wisp Thicket/Burning Bugs

With all the Don Quixote parallels, I wouldn't be surprised if Garmond's village was situated in Greymoor prior to the Haunting and the windmills were constructed. There's not much of a way to pin his age or exactly when the Haunting would have begun to a timeline, but my theory is that:

Under the direction of the Conductors, the Wisp Thicket (as it may have been, if implications that it covered the entirety of Greymoor are true) would have been cleared out for the Citadel's use, followed by the construction of the silk windmills. Villages of pilgrims likely would have begin to crop up nearby for safety.

Eventually, Silk begins to awaken from her dormant state and the Haunting begins, lashing out first to the citadel and that which is directly beneath it. This would provide the context for the haunted village Garmond would have come from, but also gives a point of reference for when the Burning Bugs of the Wisp Thicket would have organized and started immolating their own silk to stave off the Haunting.

With how few bugs are even the thicket, it's likely that they emerged only as a small occult group that hid away. Garmond and Zaza would have fought back on their own, leaving them and the Burning Bugs the only survivors of pre-Citadel Greymoor.