FAQ to the rescue–im glad i looked this up
Why is there a difference between what Moment and Apple’s Screen Time are reporting for my phone usage?
Moment and Apple’s Screen Time track your phone usage in a slightly different way. Apple counts your raw screen time. If your screen is on, Apple is counting that. Moment sometimes ignores the time when your screen is on.
For example, if you’re in another room and you get a notification, your screen will light up for 15 seconds. That 15 seconds counts in Apple’s Screen Time, but doesn’t count in Moment. The average person gets 150 notifications per day, so that adds up to a lot of screen time, even if you weren’t actively looking at your phone.
Also, Moment lets you exclude some apps from counting in your total screen time. The most common example is navigation apps (Maps, Google Maps, Waze, etc). By default, Moment doesn’t count screen time while your phone is charging, so your 2-hour drive using Maps doesn’t count for an entire 2 hours worth of screen time. Your eyes were hopefully on the road, not your screen.
Because of those reasons, Moment will usually be a bit lower than Apple’s Screen Time