@seldo Well if you choose the Mastodon.social instance, that it your local community.
This is why it's good to choose an instance that lines up with those you wish to be exposed.
Or you can even create your own instance (self hosted or managed) so that you control who is in the local instance community.
@seldo
In regards to seeing your posts on his local timeline?
The whole concept of the local timeline is to see random posts from random people on your instance, so if you delve in there then expect to see all sorts.
Especially on the general purpose Mastodon.social instance.
As long as the posts don't go against the instance rules then it's fine.
Mastodon.social has no rules on CW for instance, so both of yee can complain but it's up to each person to decide what they ultimately want to do.
@seldo
Also if you are posting publicly then you are opting in to be on the federated and local timelines.
You can always change your post privacy to unlisted to remove yourself from those timelines.