The mark of immaturity is having poor insight and judgment.

Examples include:
-Not being able to understand that Riot is a company out for profits not out for your personal satisfaction. (in other words: world does not revolve around you)
-Thinking that 4chan memes are funny and original.
-Downvoting properly reasoned arguments solely because you disagree with them.
-Unable to understand even basic sarcasm or satire.

The thread you linked is basically the opposite of that because the OP managed to trick (or troll) HoN players into spamming the LoL forums and trolling all of you while simultaneously accomplishing a good thing. This is a level of complexity that only a mature individual could deal with.

No, you simply lack the capacity to distinguish between artful trolling and artless trolling. This is called immaturity.

It's ignorant to say that all trolling is immature. The world has had a great run with trolling in the forms of Dada, A Modest Proposal, the Ems Dispatch, the Sokal hoax, Ann Coulter, WBC and Stephen Colbert among many others.

The most important quality about artful trolling is that it usually accomplishes something other than just provoking a reaction out of somebody or the execution/underlying idea is so cool that it's worth admiring even if it didn't really accomplish anything cool. Trolling isn't just about being a **** to people. You have to do it right and the ones who know how to do it right are the mature people. You will understand what it means when you become more mature. It's just something that happens for many people roughly around the time when they realize that fart jokes are not the epitome of humor.