Third party in this case is referring to Cloud wallet. you first party, Me Second Party and your cloud wallet hosting 3rd. So taking you out of the equation 2. Just language, the idea is the same.
You need to try it to understand it I guess.
You have 20 XPY in an XPYStaker wallet, Use it as collateral and then try to withdraw your coins, see what happens. Message: "Your XPY is locked due to BTCLend Active Loan"
Pay of your loan, Try again to withdraw, see what happens now. Nothing, locked was removed.
Simple isn't it?