I can think of a case where the behaviour as it is now is better.
You want to share a post with a user. So you want to first check if they are able to read the post. The popup tells you that you need to check if the user is in the trust level 1 group. So you check one group and konw wheater they can read the post.
If you also show all higher trust level groups it creates the impression, that you would have to check all of them. But everyone in the trust level 2 group is a member of the trust level 1 group, so there is no need to check that.
The message does not say “visible to users with trust level 1”. It says “visible to all memers of the group trust level 1”.