When you analyse what they said, it's very possible to say that they said that genuinely without having read the manga before.
It's possible that Matt directed Manganiello toward the wikipage (where he read the entire story of Crocodile).
If we look at Lera instagram post:
We can see that was clearly was not aware of the type of character she would be interpreting aside from the fact that she was an emotionnal character. But she made her research so it safe to say that those words were sincere.
I think they will both do a great job.