That's how events work.
First of all, your link doesn't work.
Then, events will trigger and their action will apply EVERY TIME their condition is true.
If you check if the value of a global variable is 0, it will check it every tick. And every tick its condition is true, its action will be applied.
In that case, use this variable only for this case (don't change its value anywhere else in the code) and simply make the first action of the event to modify the value from 0 to 1.
This way, it will not execute again.
Also beware if you reset global variable, then this event will trigger again.