A single shop is not a good gauge of price levels. If they feel they have too much of a certain product they will lower price on it for fear of overstocking.
In general I wouldn't be surprised if Fuji tried to sell dearer their slide film, considering that it is sold cheaper as Agfaphoto. It would be a very normal case of brand-price segmenting, when you sell two almost equal goods with small differences, brand them differently, and "target" them to two different market segments. It is done all the time, from cars to chocolate, so it would be conceivable that it is done also for slide film.
Maybe Fujifilm is licensing the Agfaphoto brand to operate this market segmentation; or maybe Agfaphoto has a deal with Fujifilm, Agfaphoto buys at least X quantity of film but Fujifilm moves the price of its own products a step higher, etc.
The same fine tea cookies which are sold in a luxury packaging are sold by the kg at a much lower price...