You are correct: I neglected to mention "on-attack" effects. The act of casting your Basic Attack will trigger a select number of effects, such as Pix (as well as some stack-generating effects). Casting an ability like MF or Ezreal's Q does not trigger these effects.
It is worth noting that "attack modifiers" are sometimes set-up incorrectly and also do not trigger attack effects. For example, Ashe's Q and Xin Zhao's Three Talon Strike both (at one point) didn't count as "attacking" for the purposes of things like Pix or Guinsoo's. Some effects, such as Lucian's innate, count as "attacking" multiple times. It is worth stressing that attacking is distinct from dealing an instance of basic damage.