This is how you should be making a thread

This way your thread will should under leo threads or your own comments here
@trouvaille/comments
This is the correct and only way to make a thread.
However if you click the Post button

Then this interface opens

This is similar to hive.blog ecency.com or peakd.com front ends
You are supposed to use this only for log blog post and the post you make shows under your posts.
So instead of making a thread you created a post so this happened.
I would discuss this issue with the team and come back to you with their suggestion.

@anomadsoul can you suggest a way out of this situation ?