Can I get free Lamborghini without risking losing anything?
Nope, you must wager at least 0.005 BTC to get 1 golden ticket, buy one or deposit 0.05 BTC.
You can get 1 free Golden ticket for every 0.05 BTC you deposit. As you don't have to wager that, so the tickets you get are free tickets.
By the way, this opportunity is not always available.