I read an interesting book some time ago by a German soldier (actually he was French, fighting for the Germans) who was on the Eastern front.
He mentions using the Panzerfaust which was really effective on Russian tanks. I suspect this is a development of that weapon.
Sure, the panzerfaust 150 looks a lot like an RPG. The earlier versions were much more primitive, single shot "sticks" without aiming mechanism. The later RPGs incorporated rocket propellant as in the US bazooka, with the warhead and weapon design of the panzerfaust 150.
The US (which invented the bazooka during WW II) copied back the improved German version, the panzerschreck, as the 3.5 inch bazookas used in Korea. The earlier US 60mm versions proved inadequate against Russian tanks.