Though I can't call it direct cheating, it was definitely a manipulation. He isn't respecting the manager's rules and not delivering for what he has paid. I don't know why he has been doing this when he is free to make posts anytime. Manipulating posts is really shady behaviour.
This type of activity could lead to managers not allowing edited posts to count which IMO I think would be great. Is he cheating? Technically no, but other managers may not feel the same way. Depends on the rules for the most part.
As a manager you can add this rule if you like, but I believe a post can be edited if necessary. But not like Saint-loup's manipulation. Due to various reasons, we might need to edit posts sometimes; it doesn't mean everyone is manipulating it.
This is something that we don't have exactly covered by the rules but burst posting sort of covers it. It is done in a way that is very difficult for us to catch since we are obviously going through posts on deadline and I would bet he isn't doing it in the threads which we frequent often, like paid pools and competitions. This also explains why he doesn't write in these threads a lot which was always a bit curious to me since they provide best place for sports discussion whitout spam and he is part of all of them.
That's why it's very important to visit users' post history and posting behaviour occasionally during the campaign before the final post count. So it will make sure quality of the posts and campaign as well; it will deliver the best results for companies.
When I had been managing campaigns, I occasionally visited participants' posts history. Because it's the manager's responsibility to deliver better quality to companies.