I agree with that. Noah is best inside because the majority of his assignment is reacting to the guy in front of him and sticking with him. He's not as effective outside with more variables in play, including whether to watch the receiver or the quarterback's eyes.
Also, on those longer routes down the sideline Noah has very poor instincts in regard to looking for the ball and finding the ball. He might technically have his guy covered but the quarterback can mostly ignore that and throw it anyway because it's a one-on-one situation with no other risk.
Everything happens quicker on the inside. Noah's lack of instincts aren't as detrimental. If he's got tight coverage on a crossing route the quarterback is likely to look elsewhere, as opposed to risking a deflected ball that lands in the lap of a safety. The shorter routes have less dispersion in terms of when the ball will arrive so Noah can watch the receiver's eye and hands to time the slap away.