In Chapter 2, the advisor mentions catapults during the monologue about building the workshop at Bibrax. But in the unit construction tab there are only siege towers and scorpions available to build. Is the reference to catapults just a minor error or loose end?

Ballistae are in fact a form of Catapult, as odd as that may seem at first if you have been conditioned to think different after playing lots of games where the term catapult is often synonymous with an Onager\Mangonel. So a Scorpion can correctly be referred to as a type of catapult.

You're right - there is a lot of overlap in the terminology. But using two different names for the same unit can cause confusion, which is the last thing you want in a game tutorial. It's a minor item, but I wanted to make they were aware of it.

yeah, and the scorpion can only be used against units, not cities, afaik, and the tip leads you to believe the artillery is for the city