Risked BTC amount is money that the person could have stolen or did steal. For example, if you do a currency trade where the other person sends first, your feedback for them would have 0 risked BTC and their feedback for you would have risked BTC equal to the BTC value of the trade.
Second sentence is only an example. It does not mean that it has to be a currency trade, just an example...
If the facts are true, and it seems that you do not even deny them ; you actually did steal that amount of btc from TF.
Does not matter anyway: trust rating are not moderated.