I know people in the industry, and hemp with significant amounts of THC commonly occurs. Unless people in the past were selecting for low THC on purpose, it's likely that THC content in hemp fluctuated and was significant enough to smoke.
I've also purchased hemp for the purposes of consuming CBD, and it got me high.
Cannabis extracts like charas - hash that is made from the resin have been around for thousands of years, and are way more potent than "narcotic skunk mutants".
Sure, but plants grown primarily for it's fibers wouldn't have anyting near the THC levels of the skunk mutants grown for narcotic use today