It's actually not all that unusual.
For Maggie, all food items are cracker, and all drink items are water. She also uses the phrases "Is that good?" and "Want some?" in context...
My CAG will ask me, "are you thirsty?" when he wants something I'm drinking. Why? Because that's what I asked him when I offered him treat cups with juice in them. He learned it in context. Tusk also uses "is that good?" and "Want some?" In context. BUT he also takes it a step further. If I'm eating bread, or a sandwich, he will say, "Want some bread?" He says "Who wants a French Fry?!" any time he sees you eating one. And he also says "Wanna chip?" So he clearly associates the words and the favorite food products.
Kiwi actually came out and said "Can I have some water?" and then said "Thank you." when she finished drinking. I didn't teach her that. My guess is she learned it from watching her previous humans... or perhaps they taught it to her.