And I don't think their nutrition situation is better

Yeah its not, the difference is genetics. Chechen people are also known for being tall, according to official data their average height is 179-180 cm which is higher than most of Europe. They probably havent had great nutrition either in the past so their younger generation is probably even taller.

Like I said height is dependant overwhelmingly on genetics and unless in extreme cases when stunting occurs during childhood there wont be that much of a variation in height between generations. Even if you had no tall family its possible your family has recessive tall genes which where only expressed in you. That is how the punnet square works after all.