It's possible if the Dropbox page that you went to was set up as a web page. If it has a Username input, a Password Input and the URL is a Dropbox URL, Passwords might have been fooled by that. I suggest changing that password as soon as possible just in case it was phished.
Edit: Thinking about it, that's a really interesting way to phish for account information. I don't think many people would have thought about setting up something like that. At least you brought attention to it so it can be addressed in Passwords.