There's no imagining here, Cakebread. Oswald fled both scene's of the crime. Since Oswald didn't run out of the TSBD so as to announce the he was fleeing he did what anyone who doesn't want to get caught did. In the Tippitt murder Oswald was seen fleeing by several witnesses.
I know that in your mind you see the arch villain depicted for you by LBJ's "Special Blue Ribbon Committee".... Just like little kids can easily identify the arch villain Snidely Whiplash, in the Dudley Doright cartoons.
And since you see Lee Oswald as the arch villain, you see any action attributed to him in a sinister light.
Sitting on a stationary city bus is FLEEING... Ha, ha, ha, heee heee heee....