When you’re strumming through chords you’re not necessarily hitting all of the strings on every strum. Sometimes you’ll only hit the first note or two of the chord on the down strum. And sometimes you’ll only strum the first two or three high notes on an up strum.
This is just one of many ways to add a lot of dynamics and complexity to your strumming patterns. In this strum I like to call the Easy Country/Folk Strum Pattern you’ll see this idea in action.