Those tanks turn on a dime. If they were running beside and the driver turned all of a sudden they wouldn't have had time to get out of the way.
If they were sleeping it's pretty easy to sleep thru a tank rolling by you believe it or not. I fell asleep once on top of a roll of barbwire on top of a moving tank. Only getting 2 hours of sleep a night for several days in a row causes you to do strange things.