They didn't delete the posts from my under standing, they removed the count from your total post count until the date stated above.
The most primitive example of post padding is as explained here, members going back through "new member" threads, some as old as October, maybe even older and posting something like "welcome" "hello"
Basically a meaningless, context-less post to boost their counts.
Other examples would be posting in every sale ad "GLWS" and no other text, or "sweet item"
Just be mindful of the the content you are including in your posts, is what they are asking for