Williams is definitely not trying to be too cryptic with this title. The poem builds up to the speaker's grandmother's last words, so what the title promises, the poem delivers. The title also puts some tension into the poem. We assume from the beginning that the grandmother we meet is going to die, so we're waiting the entire time to hear what her last words will be.
Is the title too on the nose? Should it be more metaphorical or something? Not according to Williams. He was all about poems with specific but conversational language, which describes this poem for sure. So, this title totally works, because its plain, direct style sets us up for the language of the poem itself.
One question, though: why did he bother to include the detail that the grandmother is English? There's nothing in the poem about that. Even though there's dialogue, we don't hear any English-isms in her speech. Well, Williams's real grandma was English, so that's probably where this detail came from. We still wonder why he bothered to put it in the title if it doesn't pay off in the poem.