You see, this was obvious enough to most people, but it was a fact that beasts thought differently from humans. There were elements of treachery and deception in them, yes, but that was a trait limited by species.
All species were influenced by their instincts first of all, whether they thought so or not. Even humans were often influenced by instincts but draped fancy words and philosophies over it in order to seem enlightened.
It was the same for beasts. Unless they were like hyenas or foxes who were known for being cunning and treacherous, they were mostly straightforward and honest. One could even say - in comparison to humans, of course - that they were naive.
As such, Dante's act of self-introduction without hiding anything prompted them to also share their details in the same manner. It wasn't that they didn't know to guard this information, but their thought process was that it would be unfair for them to know Dante's info without him knowing theirs.
