The fact that the height of adult males with ADHD is greater than that of males without ADHD (first figure/graphs, G & H) should indicate that there is no causative link that the medication has an impact. For females, the average does not show this, but if you look carefully, the variation is bigger. The same selection bias is possible in this case.

Instead, to me it looks like there is selection bias going on. Shorter males are more likely to get MPH prescribed is an equally valid explanation.

Luckily, the conclusion makes no assertions about height either, nor does the paper make conclusions about any causative relation.