Meta announced that users on Threads will be able to see fediverse replies on other posts besides their own. In addition, posts that originated through the Threads API, like those created via third-party apps and scheduling services, will now be syndicated to the fediverse.
You should just join an instance that blocks threads.net. Fortunately there are many of such instances. Your current instance doesn’t seem to defederate any other instance, which is kind of suspect on its own.