NE vs Colts safety

[BayStateRef]

Originally Posted by APG

Because by rule, the offense in this play is responsible for the impetus of the ball even with the defense batting the ball.

Rule 3, Section 16

IMPETUS
Article 3 Impetus is the action of a player that gives momentum to the ball and sends it in touch.

The Impetus is attributed to the offense except when the ball is sent in touch through a new momentum when the defense muffs a ball which is at rest, or nearly at rest, or illegally bats:

(a) a kick or fumble;
(b) a backward pass after it has struck the ground;
(c) or illegally kicks any ball (12-4-3).

I am trying to understand the rule in lay person's terms.

Let's say that long snap had gone over the punter's head...and came to rest (or near rest) inside the 5-yard line. A defensive player dives for the ball...and knocks it out of the end zone. That would be a touchback? New England ball on the 20, 1st and 10?

Or....same situation. The ball is bouncing at the 10-yard line, heading toward the end zone (it is neither at rest or nearly at rest), when the defense tries to pick it up, but muffs it and the ball goes through the end zone. Is that a safety or a touchback?