That is exactly the one, Lola. Just with a different alphanumeric sequence at the top (which for all I know means "I have a pet cat").
It's the number from the bottom of the white landing card you filled out on the plane and gave to the man at the control station. It does not contain a code about you personally, but rather where you landed and your carrier. It keys in to the computer system they use for immigration control.
The rest, about 'no work' and what-not is self-explanatory. It all goes to establish that you are aware of immigration controls and are possibly trying to evade them.
If they did not handwrite write something like 'code 3' (or whatever) at the bottom of the stamp, then there's no prejudice.
But from what you have written, it all sounds pretty much in order. If you feel worried about entering the next time, you can always go to the consulate in the US and get an MEC, but they will ask a lot of questions and need to see your financial information.
Oh. And the 6 months spent leave thing is a constructive rule, not a legal limitation. Somehow this got vectored on the Internet as a legal thing, and now people just believe it to be true. Hope that helps!