First, as with any legal advice, it is generally better to ask a lawyer. However, since this is the Internet I'm going to say what I think anyway. :-D
2. Designing a board based off of the arduino eagle files (this seems extremely vague?)
requires you to release your board design
Your sentence is more vague than the actual statement in the FAQ. From the FAQ, I added emphasis: "Deriving
the design of a commercial product from the Eagle files
for an Arduino board
requires you to release the modified files under the same Creative Commons Attribution Share-Alike license."
Keep in mind, either of these statements would be difficult to defend on legality due to definitions:
1. Derive and Design are different.
2. This statement specifically calls out "the Eagle Files". What is less clear is, what if I "derive" a design from the PDF of the schematic?
3. "Arduino board" isn't really a defined term.
I believe the intent of this section was to keep Arduino-based derivatives
open. For example, Seeedstudio makes variants which are still open (you can download their Eagle files.)
In my opinion, I don't think this section specifically applies to a product that is ATmega328-based. I make the distinction because "Arduino" is typically defined as a prototype platform. So when you make a final product are you going to start with the Arduino Uno schematic? Or are you going to design your hardware and add a ATmega328? I think that's the difference between Derive and Design.
All that said, you must read the Creative Commons Attribution Share-Alike license and LPGL to determine what applies to the work you are doing...