"Activity" is everything other than it being posted.

 - [Your first][1] has answers from today, edits today and comments today. These all count as activity.

 - [Your other][2] has only been posted. That activity is implicit.

This is all part of the mechanism that decides what is how the front page is sorted.

  [1]: https://askubuntu.com/questions/465109/where-should-i-put-my-script
  [2]: https://askubuntu.com/questions/464651/problem-with-printing-hplip-in-ubuntu-14-04