A business deciding they're not going to allow certain kinds of messages on their public bulletin board is no more censorship than me ordering my racist uncle to stop talking trash or get out of my house.
Which is only to say that "Yes, both situations are examples of censorship."
To make the metaphor more accurate to what Twitter is doing, let's say you had two uncles, each a different color and both racist toward the other. Now let's say you picked sides and only threw out the uncle whose racism you disagreed with.
Even if you are within your rights to do that, the banned uncle (and plenty of other, non-racist folks) are right to call you out for both your hypocrisy and your own racism.