Really I find it hard to believe that someone will give you free money.
Actually they have a free lotto and the normal lotto.
In the normal lotto you can win up to 101 btcs betting 0.001. In the free lotto is just like a "faucet lotto" where you can bet to get only 1 btc with 6 numbers.
The odds of getting the 6 numbers out of 67 are 1 in 71,852,901,120 what it is almost impossible to happen. You have 0.016129 (1/67) possibilities to get one number.
1/67 × 1/66 × 1/65 × 1/64 × 1/63 × 1/62 = 1/71852901120