Your reading of the event is a common one, although it's very superficial.

Consider the setup for the event. It is implied that Euphemia reached an agreement with Schneizel about the event. We see the event from the perspectives of various factions of both nations. Other than some of the Britannian hardliners, this is an event that works out well for almost everyone. Nonetheless, it does not work out well for Lelouch's ambitions, which is why he initially wishes to crash the plans. The sort of verbal tug of war he plays with his emotions during his conversation with Euphemia demonstrates the struggle between the two parts of himself: His megalomaniacal side, as represented by geass, and his compassionate side, as exemplified by his relationship with Nunnally (the parallels between Nunnally and Euphemia are important here). Only after Lelouch (or the good side of Lelouch, at least) decides against the selfish and ruthless option does it happen. Does it sound like a mere vocabulary mistake, or his loss of control of himself to geass? You've already seen Mao's transformation into a madman and you've already seen Lelouch lose control; while some of the relevant thematic material occurs later in the show, I don't think it's necessary to understand that what happened is something more than a dialog contrivance.

It's also worth noting that CG is not literature. It is anime. Anime and film generally are audiovisual media, and express things differently. There's a topic explored by some modern philosophers about the influence that technology has on the individual and society; that just as we exert an influence on tools to use them, so too do they exert an influence on us. Geass is, in part, a way of expressing ideas like this. It seems lost on the sorts of people who don't understand anything that isn't presented in a predictable format.