She's making the formula weaker than called for, which would be dangerous to do all the time, but I think that one bottle like that at night for a 9 month old isn't dangerous. It's no different than offering water really.
It IS dangerous to use LESS water than called for because that makes it super concentrated which can be hard on baby's kidneys.
I do think he is probably hungry. What would happen if you reversed it? What if you gave a full strength bottle first and then a weaker one later?
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)