Obviously your blockchain wallet got hacked. Always use a strong password and 2FA authentication. Now the hacker has the private keys of this address, 16Xdh8p7tdeQ446FJmuZ2T6QoNWTuZQNsW, stop using this address and if you have multiple addresses in your blockchain wallet then all of them.
Generate a new address, but before that change your password and enable 2FA.
PS: Blockchain is a bit buggy, but in terms of security it is good, have been using it for three years, no hacks, nothing. If you are using a weak password then you will get hacked no matter which wallet you are going to use.
3- If I was the thief, I would take everything. Leaving dust behind make no sense.
When my computer was hacked, I had 2.8 coins in my hot wallet. They stole 2, but left 0.8. :/
That was some generous hacker