Zechariah 9:9 explicitly announces Zion's coming King as righteous, bringing salvation, humble, and riding on a donkey. The Gospel writers directly apply this verse to Jesus' entry into Jerusalem (especially Matthew 21:4-9 and John 12:14-15). The particular emphasis of this record—the messiah would be just—is therefore part of a firmly established New Testament messianic fulfillment, although John 5:30 may illustrate that individual trait rather than itself quote Zechariah.
The explanation preserves Zechariah's original prophetic setting while distinguishing explicit New Testament quotation from broader Christian typological or theological application.