It he were shedding virus at that point, possibly yes, to those fairly close to him (~5 rows).
But this is not an airborne virus that would waft on air currents up and around the entire cabin and through the ventilation system.
What if he had a runny nose and left a tissue in the plane pocket?
Yes, if virus-laden this would, of course, be a real hazard to the clean-up crew. Although they usually wear gloves, a real chance of infection when they removed the gloves or touched a glove to their face.
The planes are NOT cleaned that well. My kid sat in a plane to Hawaii that someone had defecated in. It was NOT cleaned up before she sat in it.
Not sure how many of these are frequent, but the cleaning of the planes after every flight? Not on your life.