Oh crap, sorry, yeah, like ptr362 said I have the monthly subscription, forgot it gives a 10% discount on top of the current price!
They probably have the humble monthly 10% discount and forgot to take that into account.
The Dishonored Definitive Edition I linked also includes the DLC :)
I checked the link that you sent and it's the same price that steam are selling it for.
Yeah, couple quid cheaper on Humble Bundle too at the moment if you want to avoid grey market key sites https://www.humblebundle.com/store/dishonored-complete-collection