You make it sound as if the teacher was spying on the guy, which does not seem to be the story.  Being crammed in an economy airline sardine seat makes it sort of hard to avoid overlapping personal spaces.  Gets kind of hard to mind one's own business.

But also consider she is a teacher, creatures who are known for their highly honed skills of monitoring all the activity in a classroom, eyes in the back of her head, a 6th sense of who is up to no good, as well as assessing student progress with a glance over a shoulder.   Oh, and a raging innate love of kids and concern for their welfare.  Yeah, I'm thinking the dude sat in front of the wrong person!