Except an instance isn't a country. It isn't a government. This instance isn't operated by or for a government. Most instances are owned and operated by a single individual or a small group of people.

If you owned a coffee shop, and you banned someone for standing in a booth screaming racial slurs, that's not censorship. It is irrelevant how that person got to the coffee shop. It isn't even censorship for Starbucks to ban someone from all of their stores.

To make the analogy more complete. Suppose you had two entrances to your shop. Those entrances adjourn to neighboring restaurants/shops. Suppose one of your neighbors screams racial slurs in their own shop. You can't stop them except by asking nicely. Suppose they don't stop. They attract a bunch of people like themselves who scream racial slurs all day. Now, you could ban the people who come in to your shop screaming slurs through that entrance one by one sure... Or you could shut that entrance and lock it. Shutting the door isn't censorship.

You haven't made it illegal for them to scram racial slurs. You haven't imposed on their rights to freely operate their business as they wish. But you not keeping that entrance open isn't censorship.

It would be censorship if the government made it illegal to scream racial slurs. It would be censorship if you locked them out of and prevented them from using something they owned themselves... (It's not censorship for a landlord to kick a tenant out of a building they own for spray painting hate speech on the building for example).