Under Triggers, the Last Updated timestamp doesn't correspond to the last time I have edited that trigger(s), why?
Each trigger contains an attribute called "position", which defines the order that triggers fire (remember, they fire one at a time in order from top to bottom). This position attribute lives on the backend but is what's used to generate the order you see on your screen.
Creating a new trigger or repositioning an existing trigger can have a cascading effect on the position attribute for the rest of your existing triggers (both active and inactive).
Creating a new trigger and moving it up to the top of the trigger list means that the trigger with position: 1 now goes to position: 2, the trigger with position: 2 goes to position: 3, and so on and so forth.
For more information, refer to About trigger and how they work.