A lot of surviving armors were built for nobles as teens who subsequently outgrew them. Most combat tested armors were either salvaged for new suits, distributed among inheritence, or scrapped. The common landed knight in the high and late middle ages would have been indistiguishable in modern Europe in terms of height. What this study suggests is that even peasants and craftsmen would have had a good diet and healthy lifestyle. That's a new thought for sure.
Well, not that new. When one looks at the feast days in a typical calendar and other feudal commitments from lord to serf, they actually had a better deal than early 20th c. sharecroppers. IIRC, something like one quarter of the year actually was taken up by assorted feast days where the villagers could expect to be fed at the expense of the lord. They also got to keep quite a bit of their own produce. All told, they may have had a lesser tax burden than us.