Intimidating? They mention that if you sue them on copyright ground when they do nothing copyright related, they are able to claim damages. Which seems pretty fair, as the claims by the photographers are clearly in bad faith.
Links are still mostly legal in Germany, if the link is to something which is not, it’s a different situation and different from "hey, I own the copyright of my images, don’t link to them!"
We all know the purpose for which the images linked in the dataset will be used. "We are a non-profit organization and provide only a link" is akin to taking people for fools. Why can't these systems be trained exclusively on images for which people have given consent or for which money has been paid?
Links are still mostly legal in Germany, if the link is to something which is not, it’s a different situation and different from "hey, I own the copyright of my images, don’t link to them!"