We use this sentence quite often, is someone drinks weak or too thinned coffee. I would rather ask, if it means that "Coffee produced by Seth is weak" or "The coffee the Seth is drinking is weak", same in: قهوة سيث means the coffee Seth produced or the coffee Seth owns/drinks or does not matter?
This is why this looks weird to us. We are used to seeing "Your coffee is weak, Seth!", or another adjective. It is grammatically correct, for example, to say "Your coffee is a beverage, Seth!" but even substituting other words, it is hard to find a sentence anyone would actually say.