Chimney not properly sealed? Rain coming in - who pays?

So the water runs down the outside of the chimney?

Yep, you could say it like that

If the roofer has repaired the roof and the chimney (from the outside), he must also ensure the appropriate sealing. Or I am completely misunderstanding something.

Yes, that's why I'm turning to the experts here.

The roofer justifies his 1000€ offer by saying that the water was kept away by the cover hood. But that just doesn’t make sense to my layman’s mind when I look at the conditions of the construction. I see a loose foil between the paneling and the chimney wall and light shining through between the cover apron and the "chimney end." That’s where the water is coming in. I’ll try to illustrate it again with a drawing.

Well then show him that the [slide] is loose on the masonry and water is dripping between.

He did attach the shingles, right? Then he sealed against the shingles and not against the chimney? I am just an amateur too, but THAT can't be professional.

He attached the shingles, right? So he sealed against the shingles and not against the chimney? I'm also just an amateur, but THAT can't be professional.

Yep, against the shingles, not against the chimney

well then show him that the foil lies loose on the masonry and water drips between

As I said, I did. He says that's correct and if the cover were still on the chimney, no water would get in.

Before I really confront him now, I just want to know, is this botched work, or is this really how it's done?