Bava Kama 83b -- understanding the nature of nezek payment by chovel

Rashi writes on the mishna that the reason for the payment is "שהרי הזיקו והפסידו ממון שאם היה נצרך היה מוכר עצמו בעבד עברי" In other words, Rashi explains that this payment is restitution for a loss (פיצוי).
The Rosh however writes that the computation of nezek is that we look at him as if he were an עבד כנעני. This is something he can never be, so this indicates that according to the Rosh it is an obligation to pay money as a punishment but not as restitution.

-Based on shiur by Rav Lichtenstein Shlita (as i understood it...)