I don't know why you would remove your own posts. But I get a sense that maybe he has regretted a specific statement he has made and the only way to remove that single statement is to basically remove all his posts. It is a group execution with zero filtering capability.

Perhaps you could contact him and suggest that if he is planning to flush his posts to delete one or some that he regrets posting, perhaps you could suggest that he contact a hubleader to selectively remove that/those posts?