It can be difficult to measure a baby’s height (length) accurately, so there’s a certain margin of error in the measurements. It wouldn’t surprise me if the measurement at birth were up to an inch too short; they’re very balled up! However, they also grow longer very quickly in the early months. Iirc, an average of 1” per pound of weight gain is not out of the question.
Well, the baby seems nearly 3-4 pounds heavier than 5 weeks ago, so it cold be he gained 3”s based on that thinking.