Or at least, not the factory workers who assembled him.
In what actually isn’t a surprise to me at all, it turns out Roboto was not assembled incorrectly. The blame lies with whoever is responsible for putting the “L” and “R” on the shoulders. The shoulders were incorrectly labeled. (Note: that pic is of a fan-fixed Roboto, so the shoulder is actually on the correct side.)
Thanks to He-Man.org poster Skeletortilla for the news.