On rare and expensive unusuals, bp.tf is more of a record of the most recent sale(s) than it is a pricing guideline. Rare and extremely expensive hats are worth whatever people will pay for them. If somebody pays 300 buds for a Burning KE, then that's what it's worth.

If it sells again in the next 3 months, then that sale can be incorporated into a range. Until then, listing what the current owner bought it for is appropriate when it's the only valid sale.

If you're worried about it being an outlier, the most recent sale not included was for a Misty Skull Swagman's Swatter, which is above 8.1. 8.1 is barely above the old range, which can be attributed to the recent change that made Lucky Shots and Soldier's Stashes able to be equipped at the same time.