I'm just wondering if it is safe those who are giving free coins asking for private keys, and saying that it is safe they don't store it?
The usual sample is asking you your ETH balance, then a certain coins balance, and it will generate how much coins you will get based on your ETH and a specified coin balances. Then they will ask for your Private keys.
I just passed by all this coz I don't want to compromise my wallet for few tokens.
You did the right thing,do not risk your private keys to these suspicous airdrops most of them will ask for you to transfer your eth to their wallet of ask for your keys.And if you do that thats the end for you,these people will do their best to get your keys so they can easily transfer your funds to their own wallet.