When you read the title as "I wandered lonely as a Cloud," you might have done a double take. That’s because many people know the poem as "Daffodils," or "The Daffodils." The original title merely follows a standard informal practice of using the first line of a poem as its title. But this title is misleading, because you think you’re going to read a poem about loneliness, but then you get a poem about sublime happiness. Still, that’s what Wordsworth wanted, so you have to trust the man.
Some editors apparently thought the poem’s title should more accurately convey what the poem is about, which is why it is sometimes referred to as "The Daffodils." The poem is included in many anthologies, including Francis Palgrave’s 1875 collection The Golden Treasury under the title of "The Daffodils."