As long as the Custom Movement speed is anything other than 0, it will register as Moving. I'm not sure what you're doing to control the speed of the object, but it could be worth putting in an event that sets its speed to 0 if it's between -5 and 5 (or something similar).
Also, I'm not sure if you have a counter-event that sets the boolean to false under any circumstances. If not, you'll need something like that :)