First thought was BS!

Assuming the hose was hooked direct to the WH outlet, opening a hot
water faucet in the system should have drained the tank. There is
enough pressure in a column of water pushing down to suck the water out
of the pipes to let water in.

And then I thought about it. Assuming a tank in the attic (3rd floor)
that is 4ft high you only have a 4ft (about) column of water trying to
suck a 20 ft column of water out of the pipes.

Then another thought. Why wouldn't the water drain out of the faucet
on the first floor?? The hose connection provides for air back into
the tank.

I think I'll quit, my head hurts.

Harry K