First of all credits to @ShuuFleur.

1/3 unusual hat

https://backpack.tf/item/16298969018 (Sandy firearm history)

1 sale

https://backpack.tf/profiles/76561198050414618#!/compare/1762214400/1762473600

Sold for a Disco Beat Down Helmet without a Home

https://backpack.tf/stats/Unusual/Helmet%20without%20a%20Home/Tradable/Craftable/62

* Mini suggestion for Disco Beat Down Helmet without a home

This is going to be the reason why I think the value is 14 and not 17.

https://backpack.tf/item/15709120258 (item history)

https://backpack.tf/profiles/76561198359390706#!/compare/1762387200/1762473600

Seller having the Sandy firearm protector removed but no sign of receiving the helmet, not even in the item history. (But they do receive 14 key from UnusualV3)

https://backpack.tf/item/15065789788

Odd enough its in a STN bot (Unusual V3)

So most likely the hat got dumped because the seller did not see the 17 key value on the item being worth it

2 listings have it up for sale at 16 keys.

https://stntrading.eu/item/tf2/Unusual+Disco+Beat+Down+Helmet+without+a+Home

STN has this item listed for 16 keys 2.55 ref [~16 keys] and buys it for 13 keys and 40.88 ref [~14 keys]

And the one the bot is selling this item specifically is Unusual V3 bot, who also is the bot in STN with the item available for sale at ~16 keys.

To conclude, the trade was a 1:1 in unusual hats, but I think the value of this trade is based on the buyout value promoted in STN rounding up to 14 keys.