I was clearly talking about the subject in general, in response to a blanket statement against water on buildings made by tomswartz07. Of course an ancient building might fare worse. Also noteworthy is that their comment said collapse would be inevitable but all this tweet says is "might weaken the structure."
It's not so much that it's an ancient building, it's that its structure is heavily compromised by the fire. It might fare better against an assault of water than lots of modern buildings. You can imagine one of those big warehouse spaces could fold up like a house of cards under an assault.
The larger point is that by the time you release high enough to not concentrate a huge amount of force from the water on the building, you're just not doing that much, not that much more than a really heavy natural downpour for a few seconds (which wouldn't be nearly enough to put out a fire this large).
And the trees aren't an apt comparison because the trees aren't taking the brunt of the water; the ground is. However, the roof of the structure would be taking the entire brunt of the falling water. Several tens of thousands of pounds times whatever speed its falling at squared equals a lot of kinetic energy.
