How to stop getting these tweets?

I have a twitter account. I am getting tweets from someone but he is not in my following and followers list.

I want to know how am I getting these tweets? and how to stop getting these tweets, I don’t want to block him?

It may be that you have used your twitter account to register in any other website or access services. These days most of the sites permit registration through Twitter, Facebook and LinkedIn account. These sites ask us to permit them to post tweets in our account, we allow them for it and registered in their website. So, it happens in your case as well.

You can install Slipstream Extension which lets you filter tweets for your problem.