It's not wrong to call them slates.
Stone slate is fine too.
Just because it's Yorkshire doesn't mean it's york stone. The picture isn't definitive .
However if it is a York stone roof there is nothing wrong in calling them York stone slates.
Just as a Purbeck stone roof can have a Purbeck stone slate split from a suitable bed.
Burlington stone is referred to as slate likewise Westmorland green stone ..
So to pull someone up for using a general term is petty.
Stone slate is fine too.
Just because it's Yorkshire doesn't mean it's york stone. The picture isn't definitive .
However if it is a York stone roof there is nothing wrong in calling them York stone slates.
Just as a Purbeck stone roof can have a Purbeck stone slate split from a suitable bed.
Burlington stone is referred to as slate likewise Westmorland green stone ..
So to pull someone up for using a general term is petty.