Imported topics appear on the /my/activity/topics page and not on the /posted page for users other than myself.
Imported posts also appear under /my/activity/replies but corresponding topics do not appear on the /posted page for users other than myself.
I have also confirmed through an example topic. The user_id on /t/xxx.json matches the user id on /u/yyy.json but topic xxx does not appear on /posted for user yyy
I can also try running the code you provided but there doesn’t seem to be a reason to think this is an ownership problem as far as I can tell.