It is perfectly possible that most men grow between 19 and 20. According to the chart, one can expect a growth between 0.5 mm (1/50th of an inch) for the shortest people, to about 5 mm for tallest (1/5th of an inch). I highly doubt even 5mm is perceptible at all. So for all intents an purposes, no notable growth happens, even if, technically, men continue to grow.
You can't expect anything for an individual based on a chart. My older brother was 5'11 in 9th grade and is still 5'11, same with my best friend from HS (he was actually 6'0, but didn't grow after 9th) I was probably 5'4 in 9th grade and continued growing to 5'10 at about 19-20 years old. To use that chart to say that Exum couldn't have grown an inch is just idiotic. That chart takes a huge population and plugs it into a formula to show the growth curve.