You’re right, just did a bit of fact checking myself - The Panzerlauf was used on German tanks as secondary armament. As the MG 42 was ill-suited for coaxial mounting due to the method of barrel change, the MG 34 Panzerlauf was born. The Panzerlauf had a heavier, almost solid armored barrel shroud, almost completely lacking the ventilation holes of the original MG 34.
What is kind of odd is that the kit has the standard MG34 mounted coaxially (and in the hull), but the Panzerlauf mounted on the cupola as an option - counter-intuitive i think?