A quick search shows that it is indeed an MZ,Yamaha based engine.That yellow bike may be a MV agusta, not MZ. Big single thumper motor.
their 2 strokes in the 1950's were very advanced and way ahead of the japaneseMZs were produced in communist East Germany and after the fall of the iron curtain have become an established small to medium motorcycle builder.
Amazingly in the 50s and 60s MZs were sold by a German catalog retailer named Neckermann. Think Sears here or Montgomery Ward's.
The sixties bikes have very unusual pressed sheetmetal styling which today looks kinda cool but was the kiss of death if you were seen on one in 1970.....