How does Sam Know?

[Nerwen]

Inziladun, I'm guessing dasbill is talking about the equivalent scene in the film. In that version–

1. Faramir has already learned of the Ring (from Gollum) and is determined to take it

and

2. Sam does say:

"You want to know why your brother died? He tried to take the Ring from Frodo!"

So yes, there is an issue. Obviously it's just a bit of carelessness on the part of the screenwriters... for an in-story explanation, I suppose you could say Sam's just yelling random stuff in the heat of the moment.