Many buyouts are set to 5.6 (+- fluctuating) because that's the current price here (so we got some influence^^). Also many were unboxed the last days...

http://www.tf2outpost.com/trade/5003129 - 2 months old. got offers of ~4 buds back then but no recent offers.

http://www.tf2outpost.com/trade/7081350 - Offer of a scorching hound dog (~4.3) + sweets, owner declined because he works with backpack.tf price

http://www.tf2outpost.com/trade/5945458 - 1 month old. p.e eflin deal + s.fish (~3.5) but no recent offer.

http://www.tf2outpost.com/trade/7583372 - freshly unboxed, another backpack.tf buyout

http://www.tf2outpost.com/trade/7553551 - B/O 7.5 buds (before it was 9.3) --> lol

http://www.tf2outpost.com/trade/7527078 - another freshly unboxed one, b/o = backpack.tf

http://www.tf2outpost.com/trade/7559547 - another freshly unboxed, b/o 6 buds

http://www.tf2outpost.com/trade/7222109 --> http://www.tf2outpost.com/trade/7225708 - link 2 was more recent so maybe he sold it for 3 buds. Freshly unboxed, could be a quicksell (or just dumb), not sure what happened.

http://www.tf2outpost.com/trade/7282314 - the guy who bought it got a backpack.tf buyout and unusual offers of 4+

http://www.tf2outpost.com/trade/7501820 - newer trade, still a 4+ in unusuals offer from the same guy

http://www.tf2outpost.com/search/66292787 - Outpost search

Conclusion: Just unusual offer of 4+ buds in the last 2 months and not so much traffic on the trades. High range at 4 seems fair considering an overpay in unusuals.