That's a really unhelpful comment. Please specify what encryption you think Dropbox is doing on the passwords and what knowledge you have on the topic.
I'm pretty sure you're going to say "they do TLS" and then the person you're talking to can go ahead and explain that the encryption LastPass/1Password does protects an entirely different threat model, but unless you have a conversation here no one is going to be able to communicate a thing.
To be clear, I don't owe you or anyone anything with regards to this conversation. I am not obligated to conform to any particular conversational strategy, and if my intention was to simply claim something was incorrect without elaborating, I am entitled to do so.
That said, I was wrong. I recalled what bcrypt does incorrectly.
Dropbox was not encrypting passwords they were hashing them.
If you stored already encrypted files on Dropbox nobody can decrypt those files provided your encryption key is good.