There's another sale here for a duped darkblaze pompom and 10 keys

https://backpack.tf/profiles/76561199055929199#!/compare/1643241600/1643587200

The pom has a sale here for likely all the items you see in the second compare (at least most of the keys, the topper and the hats you see in the first compare)

https://backpack.tf/profiles/76561198322957656#!/compare/1643414400/1643500800 inspecteur, norman and a few keys

https://backpack.tf/profiles/76561198322052033#!/compare/1643414400/1643500800 other side, showing keys, topper and reel

The herald that was also bought in the first compare was bought with 420 keys:

https://backpack.tf/profiles/76561198281862232#!/compare/1643414400/1643500800

Given that in the first compare, 300 keys and the pompom were removed, it is likely that the topper and the reel hat were qsold for extra keys to buy the herald, where they roughly coincide with the missing ~120 keys (along with the majority of the other keys you see disappearing there).

Even using sellers on the outdated hats (reel was in-date), that is going to put the pompom so far below 1000 that the sales here will simply be too discrepant to price this.