There's actually a large number of hobbyists who "collect" sightings of specific airliners.
Incident where a British one was arrested by the Greeks or something a couple years ago, I think....
Not to sound paranoid or anything, but the guy in the rented van looked very foreign.
Admittedly, it could have been somethign innocent as you mentioned.
But he kept looking nervously at every car that went by, and hid the camcorder when I slowed to look at him.
(I still had my short military haircut at the time.)